Swimming Pool Water Treatment

Introduction

We all love our swimming pools to cool off in the summer or to get our exercise if the knees got wonky. But underneath every swimming pools is a water treatment plant which filters and disinfects the water to make sure it is not harsh on the eyes and will not get the kids sick. The pH needs to be controlled too and the TDS (amount of dissolved salts in the water). Chemicals are sometimes needed and there are chemical free approaches.

Parameters To Control In Swimming Pools/Quality Control:

1. Control the pH of the water so it is not irritating to the eyes of swimmers. Low pH can be corrosive to any steel pipes used in the system. Higher pH renders the chlorine less effective.

2. Control bacteria and algae using biocides and algaecides or simply a cover to block the sun. Chlorine (solid, liquid or gaseous), bromine, iodine can be used as well as Ozone, and Hydrogen Peroxide.

3. Filter out suspended solids or hair/fibers/leaves so that the water is clear. Hair strainers, Sand filters, pre-coat diatomaceous earth filters, Micro and Ultra Filtration can be used.

4. Control the smell of chlorine if it is the used biocide. When chloramine levels rise, break point chlorination or super-chlorination is needed. Ammonia reacts with chlorine in the water to form chloramines. Chloramines are oxidized by excess chlorine into Nitrogen gas.

More Parameters

5. Control the chemical balance of the water so that it is neither scaling nor corrosive. Calculate the LSI (Langlier Saturation Index) make sure the water is not corrosive to tile cement or too scaling for the pipes and fittings.

6. Remove colour causing compounds or elements from the water.

7. Certain surface film forming chemicals can be added to swimming pools to slow down the process of evaporation in hot climates.

8. UV lamps kill bacteria without the use of chemicals. In combination with Peroxide, they are really powerful disinfection and organics oxidizing tools (the process is known as Advanced Oxidation Process or AOP).

9. Chemical Free swimming pools use plants and biofilters to remove N and P from the water which are needed for bacteria and algae to proliferate. Biofilters create a Biostable water.

10. When the TDS (Toltal Dissolved Solids) become too high, fresh water needs to be added and the old water removed. RO technology can be used to recycle blow down water with high TDS.

11. Take occasional samples for TVC (total viable counts) and E Coli fecal indicative bacteria.

Chemicals Used

For pH control, various acids and alkalies are used such as Hydrochloric acid and soda ash. If sulfuric acid is used, you are adding Sulphate ions keep an eye out for Calcium Sulphate scale.

For disinfection/algae control, various oxidizing and non-oxidizing biocides can be used as well as UV light disinfection. Even ultrasonic disinfection can be used such as Ashland’s SONOXIDE technology.

Suspended solids can be filtered out using sand filtration as mentioned, pre-coat filters which use diatomaceous earth, microfiltration or ultrafiltration. Ofcourse a pump of suitable size has to be selected so that the water turn over rate is sufficient depending on the use (adult versus children’s versus baby pools). Note that sand filters need backwashing and use more water.

A strong chorine smell could be indicative of overdosing of chlorine or of formation of chloramines which are formed from the reaction of ammonia with chlorine. To remedy this situation chlorination beyond the break point of chlorine is needed which means additional chlorine is added to break down the chloramines.

Water Balancing In Reference to Hardness Scale

For balancing the water, calcium rich compounds such as lime or calcium chloride can be added or carbonate rich compounds such as soda ash can be added. A scaling water will form scale in the pipes and on the fittings. A corrosive water will leach out the calium in the cement that glues the tiles together. It is also possible to use softeners in case of hard water.

Colour causing compounds could be Natural Organic Matter such as humics or transition metal compounds such as ferric or manganese. These can be oxidized, or coagulated/filtered. It is also possible to use weak anion exchange for this.

Activated carbon

Sometimes dust-free activated carbon powder for chloramine reduction is used in diatomaceous earth precoat filtration and moulded carbon pellets for residual ozone destruction in the gaseous phase in the indoor swimming pool.

Chemical Free Swimming Pools

Yes it is possible. Chemical free swimming pools normally use some kind of Biofilter which can remove N and P from the water. This is the same principle used in aquariums to filter the ammonia that the fish release. Some kind of suspended solids filter is used to keep the water clear. A UV disinfection system can be used to keep E. Coli numbers down. Some chemical free swimming pools like to have plants around the periphery and we all know that plants love to metabolize N and P.

chemical_free_swimming_pool

Suppliers

Pentair is one of the most respected EU swimming pool water treatment equipment suppliers. Bayrol is another name that stands for German quality. Atzwanger is another EU name that inspires respect.

Professional Standards

BS EN 16713-1:2016: The Standard for Domestic swimming pools. Water systems – Filtration systems. Requirements and test methods.

Pool Water Treatment Advisory Group

NSF

Conclusion:

I personally feel that swimming pools are a luxury for the rich and a waste of energy and water resources. Why not go for a swim in the sea or river/lake? But if you must have one, then treating the water is not that complicated really.

See, It is really simple!

Kremesti Environmental offers technical and commercial/strategic consulting on all things water treatment.

Rami E. Kremesti M.Sc., CSci, CEnv, CWEM

Last updated February 22, 2025