One can distinguish private and public ones; the private ones are usually outdoors; for the public ones we can distinguish those outdoors, those indoors, and complexes with both.
In some parts of the world, a swimming pool for private use is considered a status symbol. Swimming pools can be constructed either above ground (generally constructed from plastic and metal), or in the ground (usually concrete lined). Swimming pools generally contain water to which much chlorine has been added to prevent the growth of bacteria and algae. The alternative to chlorination is to have a salt water pool.
The correct management of a backyard swimming pool is a difficult and time-consuming task. The chemical balance of the water has to be carefully monitored to make sure that it does not become fouled with algae, or grow too much bacteria. Either of these will make the water smell and look unpleasant, and can be a serious health hazard. The water must also be kept clear of debris such as fallen leaves and sticks, as these encourage fouling, and they become very slippery and dangerous as they start to decompose. Most people keep their pool either covered over or drained entirely during the months of the year in which it is not in use, as this is the easiest way to keep it sanitary. Public and competitive swimming pools are generally indoor pools - covered with a roof, and heated - to enable their use all year round.
Public pools are often found as part of a larger leisure centre or recreational complex. These centres often have more than one pool - for example an indoor heated pool, an outdoor saltwater or unheated chlorinated pool, a shallower 'children's pool', and a paddling pool for toddlers and infants. There may also be a sauna area.
Many public swimming pools are rectangles either 25m or 50m long, but a backyard pool can be any size and shape desired. There are also very elaborate pools, with artificial waterfalls, varying depths of water, bridges, and island bars; they may belong to a hotel or holiday resort.
Swimming pools designed for competitions are required to be a certain length and depth to guarantee that a 200m race will always be 200m long. Many public swimming pools are 50m long and 25m wide which is a requirement for Olympic and World Championship swimming. Professional pools also require a minimum depth of 2m, which is less common in general public pools and there are also regulations about other characteristics such as temperature, guttering and lighting as defined by FINA. Public are generally indoor pools - covered with a roof, and heated - to enable their use all year round. Competition pools have to be indoors to comply with the regulations regarding temperature, lighting and to protect the needed Automatic Officiating Equipment.
An 'Olympic Swimming Pool' is 50 metres in length ("long-course"), but recently "short-course" swimming events held in a 25 metre pool have become popular (if not held at the Olympics). There also exist many pools 33 1/3 metres in length, so that 3 lengths = 100 metres. This is sometimes jokingly referred to as "inter-course". 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.
In the US and UK pools measured in yards are still common. US yards pools tend to be fractions of 100 yards (25 or 50), whereas UK pools are more likely to be based on 110 yards. However, the international standard is metres, and world records are only recognised when swum in 50-metre pools.