chemical wastes, pollen, spores, bacteria and so on, that are blown into the water by the wind. Swimmers carry other pollutants into the water: sweat, suntan oils, urine, bacteria, viruses, etc.

Every swimming pool has a circulation pump and filter. The filters most common these days are sand filters, and are much easier to maintain than the earlier diatomaceous filters of a few years back. The pool pump ensures that the swimming pool water moves through the filter every day, thus removing unwanted pollutants and disinfected organic materials as quickly as possible.

Other common pool filters include DE (diatomaceous earth) filters, which are able to filter out finer particles of dirt, though they require more maintenance. Cartridge filters are also quite widespread and are quite simple to maintain. Nowadays a filter sand substitute containing zeolite is

gaining in popularity. The zeolite (specifically the clinoptilolite mineral) is able to filter particles as finely as DE filters in addition to having a capacity to absorb ammonia and its complexes (reducing combined chlorine and offensive chlorine odours), while not requiring any extra maintenance.

Generally, the swimming pool pump should run for at least 6-8 hours each day. There is usually a timer which cycles the pool pump on and off to ensure this constant filtration. The circulation of pool water will remove floating or suspended particles of dirt from the water, but has no effect on the substances which have settled to the bottom of the swimming pool or "stuck" to the walls.

Depending on the environmental conditions and swimmer load, the swimming pool needs regular brushing and vacuuming, generally about once a week in the swimming season for home pools. With the circulation pump turned off, the walls and floor of the pool are swept with a stiff brush. When the "dust" from the brushing settles, it is vacuumed off the floor of the swimming pool. The pool must also be vacuumed after treating with a flocculant. Nowadays, there is a variety of automatic swimming pool cleaners, which suck the dirt off the walls and floor of the swimming pool whenever the pool pump is running. These are really great for pool owners who never seem to have the time for swimming pool chores.

Now that the vacuuming is done, it is time to backwash the filter. Sand filters trap dust and dirt, as the name implies, in a bed of sand. When the filter has accumulated a large amount of dirt, the water cannot pass freely through the sand and the filter loses efficiency as the pressure increases. Backwashing sends water backwards through the filter and flushes the trapped dirt out. After backwashing, you will notice an increase in return pressure to the pool, and if you have a pressure gauge, you should notice an increase of at least 0,5 bar.

With the pool pump off, turn the filter setting to "backwash". Remove the leaf basket from the weir, clean and replace it. Turn on the pump and let it run until the water coming out of the waste pipe is clear. This generally needs a few minutes. Turn off the pump and set the filter to rinse; this cleans out the pipes and prevents any dirt from returning to the pool. It also settles the sand in the filter which has been stirred up by the backwashing. Run the pump for about a minute and then turn it off. Set the filter to "closed". Open the leaf trap near the pump, remove the basket and clean out all the leaves, twigs and rubbish it may have collected. Replace the basket, set the filter to "filter" and turn your pump back to its automatic (timer) operating position.

Great! The swimming pool looks clean and the filter has been rejuvenated. Now it's time to test the pool water and adjust the pH and chlorine levels.