How a swimming Pool works
A swimming pool may look like a big basin of water but on another hot summer day in the Valley, a swimming pool can seem like the greatest invention known to man. And there really is a lot of cool technology at work in your average pool - much more than you might think.
The Basics
Swimming pools come in all shapes and sizes, but nearly all of them use a combination of filtration and chemical treatment to continually clean a large volume of water.
A typical swimming pool consists of seven major components:
- A concrete structure basin
- A motorized pump
- A filter
- A chlorine feeder or generator
- Drains
- Returns
- PVC plastic plumbing connecting all of these elements
The basic idea is to pump water in a continual cycle, from the pool through the filtering and chemical treatment systems and back to the pool again. In this way, the pumping system keeps the water in the pool free of dirt, debris and bacteria. Some pools also include heaters in the mix.
The Drain System
As mentioned above the water in a pool needs to circulate through a filtering system, to remove dirt and debris. During normal operation, water flows to the filtering system through two or more main drains at the bottom of the pool and multiple skimmer drains around the top of the pool.
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. In order to reduce the suction at each point, EURO POOLS designs typically have 3-5 main drains, some of which are placed on the walls as well. To keep people from getting their hair or limbs caught in the drain, the drains are equipped with a cover that diverts the flow of water to prevent a dangerous vortex from forming. Euro Pools furthermore comes standard with the industry leading X-PortTM drain for unsurpassed safety.
The XportTM Drain System offers the best combination of enhanced safety, and improved pool maintenance to make your pool experience easy, clean, and worry free.
The skimmers draw water the same way as the main drains, but they suck only from the very top of the pool (the top eighth of an inch, typically). Any debris that floats -- leaves, suntan oil, hair -- leaves the pool through these drains. The diagram below shows a common system.
In the system described here, the floating weir, the door at the inlet passageway, 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 strainer basket, which catches any larger debris, such as twigs and leaves. In addition to the main inlet, the skimmer system has a 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.
The water is pumped through the filtering system and back out to returns ports around the side of the pool. This system involves a lot of suction, but if the pool is built and operated correctly, there is virtually no risk of suction holding somebody against one of the drains. In a EURO pool, there are always multiple main drains as well as several skimmer drains, so if somebody or 
something blocks one drain, the pumping system will pull water from one of the other drains. This eliminates the suction on the blocked drain.
Most swimming pools also have one one more vacuum ports, which are only used in pool cleaning. These ports attach to pool vacuum cleaners, which work like ordinary vacuum cleaners except that they suck water instead of air. The vacuum ports in most pools are driven by the main pump.
After making its way into the various drains, the water flows on to the filtering stage.
The Pump
The heart of the pool system is the water pump. In a typical pump system, an electric motor spins a so-called impeller inside the pump housing. The impeller drives the water from the various drains through the filter and back out to the water inlets.
Just before it flows into the pump, the water passes through a metal strainer basket that catches leaves and other large debris that might clog up the pump.
Next, the water flows into the filter.
The Filter
Most residential pool systems use a diatomaceous earth (D.E.) filter. In a D.E. filter, water from the pool passes through filter grids coated with diatomaceous earth, a fine powder made from the chemically inert, fossilized remains of sea organisms called diatoms.
During filtering operation, dirty water from the pool comes in through the filter's inlet pipe. Gravity pulls the water down through the D.E. to catch any dirt and debris. At the bottom of the tank, the filtered water flows through the pick-up unit and out the outlet pipe.
Over time, the collected dirt and debris in the filter slows down the water flow. Pressure gauges at the filter inlet and outlet indicate the blockage level inside and alerts when it's time to backwash the filter. To backwash, the pool custodian adjusts a number of valves to redirect the water flow typically to the sewer system.
The pump and filter systems are also connected to a well or municipal water line so fresh water automatically can be added to the pool. This is necessary to replace water lost to evaporation, backwashing and "splash-out. On a sunny day with temperatures of 100 F and heavy swimmer activity, a 20,000 gallon pool as shown above could lose 50 gallons or more in one day only!
