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Large tub for hydrotherapy or pleasure

For other uses, see Hot tub (disambiguation).

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A hot tub is a large tub full of water used for hydrotherapy, relaxation or pleasure. Some have powerful jets for massage purposes. Hot tubs are sometimes also known as "spas" or by the trade name Jacuzzi.^[1] Hot tubs may be located outdoors or indoors.

In contrast to a typical bathtub, a hot tub is designed to be used by more than one person at a time, with many models accommodating four or more people. Unlike baths, soaps and shampoos are not used in wet-jetted hot tubs (although they can be used in air-jetted hot tubs). Home hot tubs are often closer in construction to standard bathtubs, while the construction of a public hot tub often has more in common with a swimming pool, of which it can be considered a type.

History

[edit]

The earliest hot tubs were calderas in which hot stones were placed to heat the water.^{[citation needed]} Therma in Ikaria has been a very popular place particularly for hydrotherapy ever since the 4th century B.C.^[2] The remains of wrecked marble bathtubs along with a prehistoric aqueduct that have been unearthed from this area bear ample testimony of the place's popularity in the ancient times.^[2]

In 737 A.D., Japan's first onsen opened near Izumo, Shimane, and centuries later, the first ryokan (inns) were built, offering food, accommodations, and soaking tubs called ofuro.

In ancient Rome, there were three types of baths: Baths at home (balnea), private baths (balnea privata), and public baths (balnea publica). The practice of bathing was so engrained that the Roman legions, during their long occupations in foreign lands, built their own baths at mineral and thermal springs in the newly conquered lands. Examples are found all over Europe.^[3]

In the 1940s, hot tubs began to appear in the US, inspired by the Japanese ofuro. Hydrotherapy pumps were introduced by Jacuzzi. Fiberglass shell hot tubs appeared around 1970 and were soon superseded by cast acrylic shells.

The plumbing of the hot tub consists of:

• A pressure system delivering water to the jets.
• A suction system returning water to the pumps.
• A filtration system: the plumbing has to incorporate a filter system to help clean the water. Some models use a separate small 24/7 filter pump while others use programmed settings of the main pumps.
• Induced air: The jets may use a venturi effect to incorporate air into the water stream for a lighter massage effect; this requires another set of hoses.
• Some models use an air blower to force air through a separate set of jets for a different "bubbly" massage effect; this is a separate system from the induced air.
• An ozone system: ozonation is a common adjunct to water maintenance, and if installed will have its own set of hoses and fittings.

Hot tubs are usually heated using an electric or natural gas heater, though there are also submersible wood fire hot tub heaters, as well as solar hot water systems. Hot tubs are also found at natural hot springs; in this case, the water may be dangerously hot and must be combined with cool water for a safe soaking temperature.

Effective insulation greatly improves the energy efficiency of a hot tub. There are several different styles of hot tub insulation: some manufacturers fill the entire cabinet with foam, while others insulate the underside of the shell, the inside of the cabinet, or both. Many manufacturers advertise the superiority of their approach to insulation, but few independent side-by-side comparisons are available. The hot tub pump and hot tub heater represent most of the power consumption in a hot tub and vary in use of power depending on their size.^[4]

Energy efficiency of portable hot tubs has been studied by the Pacific Gas and Electric Company (PGEC),^[5] leading to industry responses^[6] and interest from both the California Energy Commission and Natural Resources Canada.^{[citation needed]} California's portable electric hot tub listing^[5] include R values of thermal insulation, and standby watts.^[7][8]

In 2019 an update to the ANSI standard for energy efficiency was approved. For the first time, this new standard increases the minimum energy efficiency level for portable spas and inflatable spas.^[9][10] Hot tub covers have been shown to reduce most of the evaporative losses from the pool when not in use. With this component of heat loss being 70%,^[11] a cover with even a small R-value is able to achieve as much as a 75% reduction in heating costs when used as opposed to leaving the water surface exposed.^[12]

There are several different types of spa covers. Some covers are better for insulation and therefore are lighter on internal parts and energy efficiency. Some examples of covers are insulated, aluminum, rolling, or a tonneau.^{[citation needed]}

Since some hot tubs are not drained after each use it is necessary to treat the water to keep it attractive and safe. It must be neither too alkaline nor too acidic, and must be sanitised to stay free of harmful microorganisms. Partly due to their high water temperatures, hot tubs can pose particular health risks if not regularly maintained: outbreaks of Legionnaires' Disease have been traced to poorly sanitized hot tubs.^[13] Typically chlorine or bromine are used as sanitizers, but salt water chlorination is starting to become more common.

Sanitation can also be aided by a non-chemical ozonator.

For aesthetic reasons, and for the sanitizer to work properly, water should be neither too alkaline nor too acidic (low pH). The hardness level of the water, measured as the amount of dissolved calcium, is also important. Insufficient hardness can lead to corrosion and water foaming. The ideal range of calcium hardness levels in a hot tub or spa water should be between 150 and 250 ppm (parts per million)^{[citation needed]}

• Portable vinyl-liner hot tub: these are cheaper and smaller, and require less power, e.g. 110–120 V 15 A household power circuits in North America.^{[citation needed]}
• Roto-molded hot tubs are constructed with the shell and surrounding cabinet as a single piece. They have molded seating.^[14]
• Acrylic: these hot tubs have a cast acrylic shell, supported by a frame structure, and are usually surrounded by a skirt of either cedar or simulated wood-grain plastic. They typically can seat two to seven persons or more.^{[citation needed][15]}
• Cement: hot tubs can also be built of cement, above-ground, or in-ground like a small swimming pool.^{[citation needed]}
• Wooden hot tubs: round wooden hot tubs peaked in popularity in the 1970s, having now been replaced by modern construction methods. Wooden hot tubs are often made of redwood or cedar and assembled from vertical staves and the structure is held together like wooden barrels, with metal bands.^[14]
• Stainless steel hot tubs can be made in any shape and size and are extremely durable.^[16]
• Fiberglass hot tub: glass-reinforced polyester (GRP) hot tubs are made of a plastic matrix reinforced by fine fibers of glass.^{[citation needed]}
• Inflatable PVC hot tubs. An inflatable hot tub is an air-filled spa structure. Air is pumped into a vinyl skin that expands and creates a solid form. Most commonly round in shape.^[17][18]

Sitting in water above normal body temperatures can cause drowsiness which may lead to unconsciousness and subsequently result in drowning. The U.S. Consumer Product Safety Commission (CPSC) recommends that water temperatures never exceed 40 degrees Celsius (104 °F). A temperature of 37 degrees Celsius (100 °F) is considered safe for a healthy adult. Soaking in water above 39 degrees Celsius (102 °F) can cause fetal damage during the first three months of pregnancy.^[19]

It is also recommended to install residual-current devices for protection against electrocution. The greater danger associated with electrical shock in the water is that the person may be rendered immobile and unable to rescue themselves or to call for help and then drown.^[20]

Hot tubs and spas are equipped with drains that can create powerful suction and between 1980 and 1996, the CPSC had reports of more than 700 deaths in spas and hot tubs, about one-third of which were drownings to children under age five. In the same period 18 incidents were reported to the CPSC involving body part entrapment. To reduce the risk of entrapment, US safety standards require that each spa have two drains for each pump, reducing the amount of suction.^[21] From 1999 to 2007 there were 26 reports to the CPSC concerning circulation entrapments hot tubs and spas, including three deaths.^[22]

In 2001^[23] and in 2012^[24] the CPSC issued recalls for spa heaters which overheated and caused fires.

The Uniform Swimming Pool, Spa and Hot Tub Code is a model code developed by the International Association of Plumbing and Mechanical Officials (IAPMO) to govern the installation and inspection of plumbing systems associated with swimming pools, spas and hot tubs as a means of promoting the public's health, safety and welfare.^[25]

Poorly sanitized hot tubs have been linked to a number of diseases, principally caused by facultative anaerobic bacteria. Such incidents include hot tub folliculitis and legionellosis.^[26][27]

• 
  Bathers enjoying a hot tub in the winter in Keystone, Colorado
• 
  Wood-fired hot tub at the Adirondack Canoe Classic, Saranac Lake, NY
• 
  A hot tub at the Big White Ski Resort, Canada

• Media related to Whirlpool baths at Wikimedia Commons

Artificial water basin for swimming

For other uses, see Swimming pool (disambiguation).

 

A swimming pool, swimming bath, wading pool, paddling pool, or simply pool, is a structure designed to hold water to enable swimming and associated activities. Pools can be built into the ground (in-ground pools) or built above ground (as a freestanding construction or as part of a building or other larger structure), and may be found as a feature aboard ships. In-ground pools are most commonly constructed from materials such as concrete, natural stone, metal, plastic, composite or fiberglass, and may follow a standardized size, the largest of which is the Olympic-size swimming pool, or be of a custom shape.

Many health clubs, fitness centers, and private clubs have pools for their members, often used for exercise. In much of the world, local governments provide publicly-run pools for their citizens. Many of these are outdoors; indoor pools are typically part of a leisure centre. Many hotels have a pool for the use of their guests. Pools as a feature in hotels are more common in tourist areas or near convention centers. Many universities and other institutional communities provide pools for their members., often as part of an institution-specific athletic or recreational complex. Apartment complexes and residential subdivisions may provide a pool for the use of their residents. Private residences, particularly in areas with warm climates, may have their own pools.

Educational facilities such as high schools and universities often have pools for physical education classes, recreational activities, leisure, and competitive athletics such as swimming teams. Hot tubs and spas are small heated pools used for relaxation or hydrotherapy. Specialised pools are also used for diving, water sports, and physical therapy, as well as for training of lifeguards and astronauts. Swimming pools most commonly use chlorinated water, or salt water, and may be heated or unheated.

History

[edit]

The "Great Bath" at the site of Mohenjo-Daro in modern-day Pakistan was most likely the first swimming pool, dug during the 3rd millennium BC. This pool is 12 by 7 metres (39 by 23 feet), is lined with bricks, and was covered with a tar-based sealant.^[1]

Ancient Greeks and Romans built artificial pools for athletic training in the palaestras, for nautical games and for military exercises. Roman emperors had private swimming pools in which fish were also kept, hence one of the Latin words for a pool was piscina. The first heated swimming pool was built by Gaius Maecenas in his gardens on the Esquiline Hill of Rome, likely sometime between 38 and 8 BC.^[2] Gaius Maecenas was a wealthy imperial advisor to Augustus and considered one of the first patrons of arts.^[3]

Ancient Sinhalese built a pair of pools called "Kuttam Pokuna" in the kingdom of Anuradhapura, Sri Lanka, in the 6th century AD. They were decorated with flights of steps, punkalas or pots of abundance, and scroll design.^[4][5]

Swimming pools became popular in Britain in the mid-19th century. As early as 1837, six indoor pools with diving boards existed in London, England.^[6] The Maidstone Swimming Club in Maidstone, Kent is believed to be the oldest surviving swimming club in Britain. It was formed in 1844, in response to concerns over drownings in the River Medway, especially since would-be rescuers would often drown because they themselves could not swim to safety. The club used to swim in the River Medway, and would hold races, diving competitions and water polo matches. The South East Gazette July 1844 reported an aquatic breakfast party: coffee and biscuits were served on a floating raft in the river. The coffee was kept hot over a fire; club members had to tread water and drink coffee at the same time. The last swimmers managed to overturn the raft, to the amusement of 150 spectators.^[7]

The Amateur Swimming Association was founded in 1869 in England,^{[citation needed]} and the Oxford Swimming Club in 1909.^[8] The presence of indoor baths in the cobbled area of Merton Street might have persuaded the less hardy of the aquatic brigade to join. So, bathers gradually became swimmers, and bathing pools became swimming pools.^{[citation needed]} In 1939, Oxford created its first major public indoor pool at Temple Cowley.

The modern Olympic Games started in 1896 and included swimming races, after which the popularity of swimming pools began to spread. In the US, the Racquet Club of Philadelphia clubhouse (1907) boasts one of the world's first modern above-ground swimming pools. The first swimming pool to go to sea on an ocean liner was installed on the White Star Line's Adriatic in 1906.^[9] The oldest known public swimming pool in the U.S., Underwood Pool, is located in Belmont, Massachusetts.^[10]

Interest in competitive swimming grew following World War I. Standards improved and training became essential. Home swimming pools became popular in the United States after World War II and the publicity given to swimming sports by Hollywood films such as Esther Williams' Million Dollar Mermaid made a home pool a desirable status symbol. More than 50 years later, the home or residential swimming pool is a common sight. Some small nations enjoy a thriving swimming pool industry (e.g., New Zealand pop. 4,116,900 – holds the record in pools per capita with 65,000 home swimming pools and 125,000 spa pools).^[12]

A two-storey, white concrete swimming pool building composed of horizontal cubic volumes built in 1959 at the Royal Roads Military College is on the Canadian Register of Historic Places.^[13]

According to the Guinness World Records, the largest swimming pool in the world is San Alfonso del Mar Seawater pool in Algarrobo, Chile. It is 1,013 m (3,323 ft) long and has an area of 8 ha (20 acres). At its deepest, it is 3.5 m (11 ft) deep.^[14] It was completed in December 2006.^[15]

The largest indoor wave pool in the world is at DreamWorks Water Park within the American Dream shopping and entertainment complex at the Meadowlands Sports Complex in East Rutherford, New Jersey, United States, and the largest indoor pool in North America is at the Neutral Buoyancy Lab in the Sonny Carter Training Facility at NASA JSC in Houston.^[16][17]

In 2021, Deep Dive Dubai, located in Dubai, UAE, was certified by the Guinness Book of World Records as the world's deepest swimming pool reaching 60 metres (200 ft).^[18][19] The Y-40 swimming pool at the Hotel Terme Millepini in Padua, Italy, previously held the record, 42.15 m (138.3 ft), from 2014 until 2021.^[20]

The Fleishhacker Pool in San Francisco was the largest heated outdoor swimming pool in the United States. Opened on 23 April 1925, it measured 1,000 by 150 ft (300 by 50 m) and was so large that the lifeguards required kayaks for patrol. It was closed in 1971 due to low patronage.^[21]

In Europe, the largest swimming pool opened in 1934 in ElblÄ…g (Poland), providing a water area of 33,500 square metres (361,000 sq ft).^[22]

One of the largest swimming pools ever built was reputedly created in Moscow after the Palace of Soviets remained uncompleted. The foundations of the palace were converted into the Moskva Pool open-air swimming pool after the process of de-Stalinisation.^[23] However, after the fall of communism, Christ the Saviour Cathedral was re-built on the site between 1995 and 2000; the cathedral had originally been located there.^{[citation needed]}

The highest swimming pool is believed to be in Yangbajain (Tibet, China). This resort is located at 4,200 m (13,800 ft) AMSL and has two indoor swimming pools and one outdoor swimming pool, all filled with water from hot springs.^[24]

Length: Most pools in the world are measured in metres, but in the United States pools are often measured in feet and yards. In the UK most pools are calibrated in metres, but older pools measured in yards still exist. In the US, pools tend to either be 25 yards (SCY-short course yards), 25 metres (SCM-short course metres) or 50 metres (LCM - long course meters). US high schools and the NCAA conduct short course (25 yards) competition. There are also many pools 33+1⁄3 m long, so that 3 lengths = 100 m. This pool dimension is commonly used to accommodate water polo.^{[citation needed]}

USA Swimming (USA-S) swims in both metric and non-metric pools. However, the international standard is metres, and world records are only recognized when swum in 50 m pools (or 25 m for short course) but 25-yard pools are very common in the US. In general, the shorter the pool, the faster the time for the same distance, since the swimmer gains speed from pushing off the wall after each turn at the end of the pool.

Width: The width of the pool depends on the number of swimming lanes and the width of each individual lane. In an Olympic swimming pool each lane is 2.5 meters wide^[25] and contains 10 lanes, thus making the pool 25 meters wide.

Depth: The depth of a swimming pool depends on the purpose of the pool, and whether it is open to the public or strictly for private use. If it is a private casual, relaxing pool, it may go from 1.0 to 2.0 m (3.3 to 6.6 ft) deep. If it is a public pool designed for diving, it may slope from 3.0 to 5.5 m (10 to 18 ft) in the deep end. A children's play pool may be from 0.3 to 1.2 m (1 to 4 ft) deep. Most public pools have differing depths to accommodate different swimmer requirements. In many jurisdictions, it is a requirement to show the water depth with clearly marked depths affixed to the pool walls,^[26][27] although this may not be the case for private pools in some jurisdictions.^[28]

Pools can be either indoors or outdoors. They can be of any size and shape, and inground or above ground. Most pools are permanent fixtures, while others are temporary, collapsible structures.

Private pools are usually smaller than public pools, on average 3.7 m × 7.3 m (12 ft × 24 ft) to 6.1 m × 12.2 m (20 ft × 40 ft) whereas public pools usually start at 20 m (66 ft).^{[citation needed]} Home pools can be permanently built-in, or be assembled above ground and disassembled after summer. Privately owned outdoor pools in backyards or gardens started to proliferate in the 1950s in regions with warm summer climates, particularly in the United States with desegregation.^[29] A plunge pool is a smaller, permanently installed swimming pool, with a maximum size of approximately 3 m × 6 m (10 ft × 20 ft).^[30][31][32]

Construction methods for private pools vary greatly. The main types of in-ground pools are gunite shotcrete, concrete, vinyl-lined, and one-piece fiberglass shells.

Many countries now have strict pool fencing requirements for private swimming pools, which require pool areas to be isolated so that unauthorized children younger than six years cannot enter. Many countries require a similar level of protection for the children residing in or visiting the house, although many pool owners prefer the visual aspect of the pool in close proximity to their living areas, and will not provide this level of protection. There is no consensus between states or countries on the requirements to fence private swimming pools, and in many places they are not required at all, particularly in rural settings.^[33]

Inexpensive temporary polyvinyl chloride pools can be bought in supermarkets and taken down after summer. They are used mostly outdoors in yards, are typically shallow, and often their sides are inflated with air to stay rigid. When finished, the water and air can be let out and this type of pool can be folded up for convenient storage. They are regarded in the swimming pool industry as "splasher" pools intended for cooling off and amusing toddlers and children, not for swimming, hence the alternate name of "kiddie" pools.^{[citation needed]}

Toys are available for children and other people to play with in pool water. They are often blown up with air so they are soft but still reasonably rugged, and can float in water.

• 
  A black Labrador Retriever bathing in a kiddie pool
• 
  Children playing in an inflatable pool

Public pools are often part of a larger leisure center or recreational complex. These centres often have more than one pool, such as an indoor heated pool, an outdoor (chlorinated, saltwater or ozonated) pool which may be heated or unheated, a shallower children's pool, and a paddling pool for toddlers and infants. There may also be a sauna and one or more hot tubs or spa pools ("jacuzzis").

Many upscale hotels and holiday resorts have a swimming pool for use by their guests. If a pool is in a separate building, the building may be called a natatorium. The building may sometimes also have facilities for related activities, such as a diving tank. Larger pools sometimes have a diving board affixed at one edge above the water.

Many public swimming pools are rectangles 25 m or 50 m long, but they can be any size and shape. There are also elaborate pools with artificial waterfalls, fountains, splash pads, wave machines, varying depths of water, bridges, and island bars.

Some swimming facilities have lockers for clothing and other belongings. The lockers can require a coin to be inserted in a slot, either as deposit or payment. There are usually showers – sometimes mandatory – before and/or after swimming. There are often also lifeguards to ensure the safety of users.

Wading or paddling pools are shallow bodies of water intended for use by small children, usually in parks. Concrete wading pools come in many shapes, traditionally rectangle, square or circle. Some are filled and drained daily due to lack of a filter system. Staff chlorinate the water to ensure health and safety standards.^{[citation needed]}

See: #Dimensions (above) and Swimming (sport)#Competition pools

The Fédération Internationale de la Natation (FINA, International Swimming Federation) sets standards for competition pools: 25 or 50 m (82 or 164 ft) long and at least 1.35 m (4.4 ft) deep. Competition pools are generally indoors and heated to enable their use all year round, and to more easily comply with the regulations regarding temperature, lighting, and automatic officiating equipment.

An Olympic-size swimming pool (first used at the 1924 Olympics) is a pool that meets FINA's additional standards for the Olympic Games and for world championship events. It must be 50 by 25 m (164 by 82 ft) wide, divided into eight lanes of 2.5 m (8.2 ft) each, plus two areas of 2.5 m (8.2 ft) at each side of the pool. Depth must be at least 2 m (6.6 ft).^[34]

The water must be kept at 25–28 °C (77–82 °F) and the lighting level at greater than 1500 lux. There are also regulations for color of lane rope, positioning of backstroke flags (5 metres from each wall), and so on.^[34] Pools claimed to be "Olympic pools" do not always meet these regulations, as FINA cannot police use of the term. Touchpads are mounted on both walls for long course meets and each end for short course.

A pool may be referred to as fast or slow, depending on its physical layout.^[35] Some design considerations allow the reduction of swimming resistance making the pool faster: namely, proper pool depth, elimination of currents, increased lane width, energy absorbing racing lane lines and gutters, and the use of other innovative hydraulic, acoustic and illumination designs.

In the last two decades, a new style of pool has gained popularity. These consist of a small vessel (usually about 2.5 × 5 m) in which the swimmer swims in place, either against the push of an artificially generated water current or against the pull of restraining devices. These pools have several names, such as swim spas, swimming machines, or swim systems. They are all examples of different modes of resistance swimming.

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Hot tubs and spa pools are common heated pools used for relaxation and sometimes for therapy. Commercial spas are common in the swimming pool area or sauna area of a health club or fitness center, in men's clubs, women's clubs, motels and exclusive five-star hotel suites. Spa clubs may have very large pools, some segmented into increasing temperatures. In Japan, men's clubs with many spas of different size and temperature are common.

Commercial spas are generally made of concrete, with a mosaic tiled interior. More recently^[when?] with the innovation of the pre-form composite method where mosaic tiles are bonded to the shell this enables commercial spas to be completely factory manufactured to specification and delivered in one piece. Hot tubs are typically made somewhat like a wine barrel with straight sides, from wood such as Californian redwood held in place by metal hoops. Immersion of the head is not recommended in spas or hot tubs due to a potential risk of underwater entrapment from the pump suction forces. However, commercial installations in many countries must comply with various safety standards which reduce this risk considerably.

Home spas are a worldwide retail item in western countries since the 1980s, and are sold in dedicated spa stores, pool shops, department stores, the Internet, and catalog sales books. They are almost always made from heat-extruded acrylic sheet Perspex, often colored in marble look-alike patterns. They rarely exceed 6 m² (65 sq ft) and are typically 1 m (3 ft 3 in) deep, restricted by the availability of the raw sheet sizes (typically manufactured in Japan). There is often a mid-depth seating or lounging system, and contoured lounger style reclining seats are common.

Upmarket spas often include a drinks tray, lights, LCD flat-screen TV sets and other features that make the pool a recreation center. Due to their family-oriented nature, home spas are normally operated from 36 to 39 °C (97 to 102 °F). Many pools are incorporated in a redwood or simulated wood surround, and are termed "portable" as they may be placed on a patio rather than sunken into a permanent location. Some portable spas are shallow and narrow enough to fit sideways through a standard door and be used inside a room. Low power electric immersion heaters are common with home spas.

Whirlpool tubs first became popular in the U.S. during the 1960s and 1970s. A spa is also called a "jacuzzi" there, as the word became a generic after-plumbing component manufacturer; Jacuzzi introduced the "spa whirlpool" in 1968. Air bubbles may be introduced into the nozzles via an air-bleed venturi pump that combines cooler air with the incoming heated water to cool the pool if the temperature rises uncomfortably high. Some spas have a constant stream of bubbles fed via the seating area of the pool, or a footwell area. This is more common as a temperature control device where the heated water comes from a natural (uncontrolled heat) geothermal source, rather than artificially heated.

Water temperature is usually very warm to hot – 38 to 42 °C (100 to 108 °F) – so bathers usually stay in for only 20 to 30 minutes. Bromine or mineral sanitizers are often recommended as sanitizers for spas because chlorine dissipates at a high temperature, thereby heightening its strong chemical smell. Ozone is an effective bactericide and is commonly included in the circulation system with cartridge filtration, but not with sand media filtration due to clogging problems with turbid body fats.

In the early 20th century, especially in Australia, ocean pools were built, typically on headlands by enclosing part of the rock shelf, with water circulated through the pools by flooding from tidal tanks or by regular flooding over the side of the pools at high tide. This continued a pre-European tradition of bathing in rockpools with many of the current sites being expanded from sites used by Aboriginal Australians or early European settlers. Bathing in these pools provided security against both rough surf and sea life. There were often separate pools for women and men, or the pool was open to the sexes at different times with a break for bathers to climb in without fear of observation by the other sex.^[36] These were the forerunners of modern "Olympic" pools. A variation was the later development of sea- or harbour-side pools that circulated sea water using pumps. A pool of this type was the training ground for Australian Olympian Dawn Fraser.

There are currently about 100 ocean baths in New South Wales, which can range from small pools roughly 25 metres long and "Olympic Sized" (50m) to the very large, such as the 50 × 100 m baths in Newcastle. While most are free, a number charge fees, such as the Bondi Icebergs Club pool at Bondi Beach. Despite the development of chlorinated and heated pools, ocean baths remain a popular form of recreation in New South Wales.

A semi-natural ocean pool exists on the central coast of New South Wales; it is called The Bogey Hole.

The Marina Bay Sands SkyPark Infinity Pool in Singapore, viewed from the poolside (left) and near the edge (right)

An infinity pool (also named negative edge or vanishing edge pool) is a swimming pool which produces a visual effect of water extending to the horizon, vanishing, or extending to "infinity". Often, the water appears to fall into an ocean, lake, bay, or other similar body of water. The illusion is most effective whenever there is a significant change in elevation, though having a natural body of water on the horizon is not a limiting factor.^{[citation needed]}

Natural pools were developed in central and western Europe in the early and mid-1980s by designers and landscape architects with environmental concerns. They have recently been growing in popularity as an alternative to traditional swimming pools.^[37][38] Natural pools are constructed bodies of water in which no chemicals or devices that disinfect or sterilize water are used, and all the cleaning of the pool is achieved purely with the motion of the water through biological filters and plants rooted hydroponically in the system. In essence, natural pools seek to recreate swimming holes and swimmable lakes, the environment where people feel safe swimming in a non-polluted, healthy, and ecologically balanced body of water.

Water in natural pools has many desirable characteristics. For example, red eyes, dried-out skin and hair, and bleached swimsuits associated with overly chlorinated water are naturally absent in natural pools.^{[citation needed]} Natural pools, by requiring a water garden to be a part of the system, offer different aesthetic options and can support amphibious wildlife such as snails, frogs, and salamanders, and even small fish if desired.

A zero-entry swimming pool, also called a beach entry swimming pool, has an edge or entry that gradually slopes from the deck into the water, becoming deeper with each step, in the manner of a natural beach. As there are no stairs or ladders to navigate, this type of entry assists older people, young children and people with accessibility problems (e.g., people with a physical disability) where gradual entry is useful.

Indoor pools are located inside a building with a roof and are insulated by at least three walls. Built for year-round swimming or training, they are found in all climate types. Since the buildings around indoor pools are insulated, heat escapes much less, making it less expensive to heat indoor pools than outdoor pools (all of whose heat escapes).^[39]

Architecturally, an indoor pool may look like the rest of the building, but extra heating and ventilation and other engineering solutions are required to ensure comfortable humidity levels. In addition to drainage and automatic pool covers, there are a number of ways to remove the humidity present in the air in any wet indoor environment. Efficient dehumidification in the indoor pool environment prevents structural damage, lowers energy costs for cooling or heating, and improves the indoor climate to provide a comfortable swimming environment.^{[citation needed]}

Some colleges, universities, and high schools have buildings that use the term "natatorium" in their names, especially when the building houses more than just a swimming pool, for example a diving well or facilities for water polo. The word natatorium was borrowed from Late Latin "place for swimming" into English in New England in 1890.^[40][41]

This type of swimming pool is suspended high above the ground. A prominent example is the Sky Pool in London's Embassy Gardens, the world's first floating pool.^[42]

Swimming pools are also used for events such as synchronized swimming, water polo, canoe polo and underwater sports such as underwater hockey, underwater rugby, finswimming and sport diving as well as for teaching diving, lifesaving and scuba diving techniques. They have also been used for specialist tasks such as teaching water-ditching survival techniques for aircraft and submarine crews and astronaut training. Round-cornered, irregular swimming pools, such as the Nude Bowl, were drained of water and used for vertical skateboarding.

Levels of bacteria and viruses in swimming pool water must be kept low to prevent the spread of diseases and pathogens. Bacteria, algae and insect larvae can breed in the pool if water is not properly sanitized. Pumps, mechanical sand filters, and disinfectants are often used to sanitise the water.

Chemical disinfectants, such as chlorine (usually as a hypochlorite salt, such as calcium hypochlorite) and bromine, are commonly used to kill pathogens. If not properly maintained, chemical sanitation can produce high levels of disinfection byproducts. Sanitized swimming pool water can theoretically appear green if a certain amount of iron salts or copper chloride are present in the water.^[43]

Acesulfame potassium has been used to estimate how much urine is discharged by swimmers into a pool.^[44] A Canadian study estimated that swimmers had released 75 litres of urine into a large pool that had about 830,000 litres of water and was a third of the size of an olympic pool. Hot tubs were found to have higher readings of the marker. While urine itself is relatively harmless, its degradation products may lead to asthma.^[44]

Swimming pool heating costs can be significantly reduced by using a pool cover. Use of a pool cover also can help reduce the amount of chemicals (chlorine, etc.) required by the pool. Outdoor pools gain heat from the sun, absorbing 75–85% of the solar energy striking the pool surface. Though a cover decreases the total amount of solar heat absorbed by the pool, the cover eliminates heat loss due to evaporation and reduces heat loss at night through its insulating properties. Most swimming pool heat loss is through evaporation.^[45]

In areas which reach freezing temperature, it is important to close a pool properly. This varies greatly between in-ground and above-ground pools. By taking steps to properly secure the pool, it lessens the likelihood that the superstructure will be damaged or compromised by freezing water.^[46]

In preparation for freezing temperatures, an in-ground swimming pool's pipes must be emptied. An above-ground pool should also be closed, so that ice does not drag down the pool wall, collapsing its structure. The plumbing is sealed with air, typically with rubber plugs, to prevent cracking from freezing water. The pool is typically covered to prevent leaves and other debris from falling in. The cover is attached to the pool typically using a stretch cord, similar to a bungee cord, and hooks fitted into the pool surround. The skimmer is closed off or a floating device is placed into it to prevent it from completely freezing and cracking.

Floating objects such as life rings or basketballs can be placed in the pool to avoid its freezing under the cover. Sand or DE filters must be backwashed, with the main drain plug removed and all water drained out. Drain plugs on the pool filter are removed after the filter has been cleaned. The pool pump motor is taken under cover. Winter chemicals are added to keep the pool clean. The innovation of a composite construction of fiberglass, with an epoxy coating and porcelain ceramic tiles has led to the pre-form, composite-type with significant advantages over older methods; however, it also has increased sensitivity to metal staining.^{[citation needed]}

In climates where there is no risk of freezing, closing down the pool for winter is not so important. Typically, the thermal cover is removed and stored. Winter sunlight can create an algae mess when a cover that has been left on all winter is removed. The pool is correctly pH-balanced and super-chlorinated. One part algaecide for every 50,000 parts of pool water should be added, and topped up each month. The pool should be filtered for one to two hours daily to keep the automated chlorination system active.^{[citation needed]}

Pools pose a risk of drowning, which may be significant for swimmers who are inexperienced, suffer from seizures, or are susceptible to a heart or respiratory condition. Lifeguards are employed at most pools to execute water rescues and administer first aid as needed in order to reduce this risk.

Diving in shallow areas of a pool may also lead to significant head and neck injuries; diving, especially head-first diving, should be done in the deepest point of the pool, minimally 2.4 m (7 ft 10 in), but desirably 3.7 m (12 ft), deeper if the distance between the water and the board is great.

Pools present a risk of death due to drowning particularly in young children. In regions where residential pools are common, drowning is a major cause of childhood death. As a precaution, many jurisdictions require that residential pools be enclosed with fencing to restrict unauthorized access. Many products exist, such as removable baby fences. The evidence for floating alarms and window/door alarms to reduce the risk of drowning is poor.^[47] Some pools are equipped with computer-aided drowning prevention or other forms of electronic safety and security systems.

Suspended ceilings in indoor swimming pools are safety-relevant components. The selection of materials under tension should be done with care. Especially the selection of unsuitable stainless steels can cause problems with stress corrosion cracking.^[48]

In public swimming pools, dress code may be stricter than on public beaches, and in indoor pools stricter than outdoor pools. For example, in countries where women can be topless on the beach, this is often not allowed in a swimming pool, and a swimsuit must be worn. For men, wearing ordinary shorts and a T-shirt to go in the water at a beach may be considered acceptable, but pools usually require real swimsuits or other dedicated water wear as swimming with regular clothes can potentially weigh a swimmer down should they need to be rescued. In France and some other European countries, board shorts are usually not allowed for "hygienic" reasons. In Nordic countries, in particular Iceland, rules about clothing and hygiene are especially strict.^[49] When diving from a high board, swimsuits are sometimes worn doubled up (one brief inside another) in case the outer suit tears on impact with the water.

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