How a pool works

The idea of a swimming pool is quite simple in engineering terms – a tank filled with water. A main circulating pump that continuously re-circulates the water, and the means to heat and chemically treat it.

The ‘tank’ of water usually has a deep end and a shallow end. The deep end is the obvious place to put the pool outlets or where the water, having been swum in (and polluted) by the bather, will leave the tank for replenishment and treatment. The shallow end is where the water returns to the pool after receiving that treatment.


Water leaving the pool is low in chlorine content. It contains bacteria and debris introduced by bathers – fluff and fibres from bathing costumes, cosmetics washed from bathers’ bodies, amongst other things. However, the level of chlorine maintained in a well run pool renders these potentially hazardous products quite harmless almost instantaneously and makes bathing safe.

The path that water takes through the treatment process.

The strainer basket is the first filter the water comes to, it is there to remove all the big particles and trap anything that could cause damage to the main circulating pump impeller – e.g. hair grips and plasters. An outdoor pool may require the strainer basket to be cleaned several times each day, as leaves and sweet wrappers can easily enter the basket and reduce the water flow dramatically.

The circulation pump sucks the water away from the pool and pushes it through the other pieces of equipment as it travels back to the pool.

The next major step is filtration. This process involves the removal of suspended particles from the water by passing it through a filtering medium such as sand or glass. Filtration of pool water via sand or glass filters is a part chemical and part physical process.

Over a period of time the filter becomes saturated and requires cleaning, this is a process known as backwashing. It is simply the removal of accumulated dirt and bacteria from the filter, by reversing the flow of water.

In normal operation mode, pool water will enter the filter at the top and flow out at its base. By opening or closing valves in a strict order, the water is introduced through the base of the filter, up through the sand and down to a waste pipe, taking with it the collected dirt. This dirty water can be seen through the waste pipe water sight glass. With the process continuing until the water runs clear.

The water, having left the filter/s, will now travel towards the calorifier (or heat exchanger). This is a series of tubes through which hot water passes from the building’s boiler system. Pool water passes over these tubes and a transfer of heat occurs.

The water returns to the pool having been strained, filtered and heated.



Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s