As we saw previously, the water in a swimming pool needs to circulate through a filtration system to remove dirt and debris. During normal operation, water flows to the filtration system through the main drains at the bottom of the pool and the skimmers around the top of the pool. Minimum 70% of the water should be taken through the skimmers. New European requirements are 100% if water is injected from bottom inlets.
Diagram of a swimming pool system
The main drains are usually located on the lowest point in the pool, so the entire pool surface slants toward them. Most of the dirt and debris that sinks exits the pool through these drains. To prevent people’s hair or limbs caught in the plumbing, it is recommended that two or more drains are installed to reduce the suction pressure. Antivortex drains and covers, which divert the flow of water to prevent a dangerous vortex from forming, can also be used.
The skimmers draw water the same way as the main drains, but they suck only from the very top of the pool. Any floating debris (leaves, suntan oil, hair) exits the pool through these skimmers. The diagram below shows a common system.
Diagram of a swimming pool skimmer
In the system described above, the floating skimmer flap, where the water enters the skimmer, swings in and out to let a very small volume of water in at a time. To catch debris effectively, the goal is to skim just the surface level. The water flows through the skimmer basket, which catches any larger debris such as twigs and leaves, and needs to be cleaned regularly to prevent clogging of the suction line. In addition to the main inlet, the skimmer system can have an optional secondary equalizer line leading to a drain below the surface level. This line keeps the skimmer from drawing air into the pump system if the water level drops below the level of the main inlet. ladder
Used by swimmers to get into or out of the diving well.
ladders and stepladders 
underwater light ...
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