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TRANSFORMING BASE SUBSTANCES INTO GOLD

 

Swimming Pool Water Treatment

White Paper by Rami Elias Kremesti M.Sc., CSci, CEnv, CWEM

Kremesti Environmental Consulting Ltd

Transmutare Substantiarum Basium In Aurum ^TM

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. There is something mystical about immersing ourselves in water. In the Jewish tradition, a Mikva is a water pool used for ceremonial immersion in water, the act behind the origin of the word Baptismos in Greek…

Parameters To Control In Swimming Pools/Treatment :

Below I compile a list of most parameters that need to be controlled in a swimming pool to maintain safety, hygiene, aesthetics and maintain the equipment and the water pool itself. We also look at how to maintain and control these parameters.

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. pH adjusters are used to increase or decrease the pH of a swimming pool.

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. Ceramic SiC filters are state of the art.

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. For this active carbon can be used or AOP’s – Advanced Oxidation Processes.

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 by removing ammonia, P and BOD/COD.

10. When the TDS (Total 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/backwash water with high TDS.

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

12. If the feed water is, say from a borehole, and it contains H2S and/or Fe/Mn, then a Green Sand filter will solve this problem. It would also be a good idea to aerate the feedwater to increase Oxygen levels and remove any odours/tastes from the water.

 

Typical Parameters

 

Nuances

The nuances in swimming pool water treatment involve a complex interplay of physical processes, chemical balancing, and advanced disinfection technologies, primarily aimed at maintaining hygiene while managing the formation of potentially harmful disinfection by-products (DBPs). The constant input of human contaminants (bacteria, fungi, sweat, urine, cosmetics, UV filters) makes pool water a unique and challenging matrix to treat effectively.

DBP’s

Disinfection By-Products (DBPs) in pools are harmful chemicals, like Trihalomethanes (THMs) and Haloacetic Acids (HAAs), formed when chlorine (or bromine) reacts with sweat, urine, skin cells, and cosmetics from swimmers. These DBPs, including irritants like chloramines, exist in pool water and air, causing eye/skin irritation, asthma, and potentially increasing cancer risk, with exposure happening through inhalation and skin absorption. Reducing DBPs involves better swimmer hygiene, increased ventilation, advanced filtration, and using alternative disinfectants like UV or ozone, alongside chlorine.

Niche Application of Activated Carbon Filtration

Carbon filters are sometimes used in specific, niche scenarios, such as:

Treating the water before it enters the pool (source water) to remove high levels of iron/manganese or to reduce TOC.

Temporarily dechlorinating pool water before backwashing into sensitive drainage systems.

Turnover Rates

Typical Turnover Times (All Water  Passes Through the Filter Once):

Residential Pools: 4-12 hours (aim for 1-2 times daily).
Public/Commercial Pools: 2.5-8 hours, depending on size and usage.
Leisure/Splash Pools: 10 mins – 2.5 hours (shallower needs faster turnover).
Spas (Residential): Around 15 minutes.

I have seen swimming pools in Bulgaria in which the child/toddler pool is connected to the main adult swimming pool this is bad design and should not have passed the health inspection.

 

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. After break-point chlorination, SBS or SMBS can be dosed to neutralize the excess chlorine.

 

Adding borates to pools stabilizes pH, reduces chlorine demand, prevents algae, and makes water feel softer and clearer, acting as a one-time treatment that’s replenished by water loss, not use. You generally add borates (like boric acid or sodium borate) after balancing pH and alkalinity to achieve a target level (around 30-50 ppm), often by broadcasting the powder or pouring it in the skimmer while the pump runs, then adjusting pH as needed. Note that this should not be practiced in Children or Toddler pools as Borate is toxic if swallowed.

Borates have low acute toxicity but become harmful in large doses, causing gastrointestinal issues (vomiting, diarrhea), dehydration, kidney damage, and neurological problems, with severe cases leading to rash, seizures, and even death, especially in infants; chronic high exposure affects male reproduction and development, though typical dietary intake is safe, with limits set by health organizations.

Water Balancing In Reference to Hardness Scale

For balancing the water, calcium rich compounds such as lime or calcium/magnesium 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 calcium 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.

Therapeutic Swimming Pools

Swimming pools with sulphide, often from natural thermal springs, are therapeutic mineral baths famous for treating skin, joint, and respiratory issues, like those in Poland (Solec-Zdrój), Hisaria in Bulgaria or Czech Republic (Velké Losiny). These pools use naturally rich hydrogen sulphide water, sometimes without chlorine due to sulphur’s antibacterial properties, offering healing benefits by improving joint mobility, reducing inflammation, and aiding skin conditions, though requiring careful management due to H₂S’s potential toxicity in high concentrations.

How H2S Pools Work & Benefits

Absorption: Sulphide penetrates the skin, forming compounds that support connective tissues and cartilage, reducing pain and improving mobility.

Anti-inflammatory: Participates in the body’s antioxidant defences, easing inflammation.

Metabolic Effects: Can help lower cholesterol, triglycerides, and uric acid.

Respiratory Aid: Sulphur in baths and springs is used for asthma and respiratory issues.

 

Health and Safety

The VGBA (Virginia Graeme Baker Pool & Spa Safety Act) US standard requires all public pools and spas to use anti-entrapment drain covers and safety systems, mandating drain covers that meet the ASME/ANSI A112.19.8 standard (or successor ANSI/APSP/ICC 16) to prevent severe suction entrapment, with required markings like “VGB 2008,” “Life: X Years,” flow rate, and manufacturer info, ensuring safer public water environments by reducing drowning and entrapment risks.

Key VGBA Requirements & Standards:

Anti-Entrapment Drain Covers: All public pools and spas must have compliant drain covers designed to prevent body or hair entrapment, according to the CPSC.

ASME/ANSI A112.19.8 Standard: This is the primary performance standard for these drain covers, focusing on preventing suction entrapment.

Successor Standard: The current standard is ANSI/APSP/ICC 16-2017, which supersedes the earlier ASME standard.

Mandatory Markings: Drain covers must display:

“VGB 2008” (for newer covers).
Manufacturer’s Name & Model Number.
Flow Rate (GPM).
“Life: X Years” (indicating service life).

With regards to chemical safety in the UK, COSHH and H&SE guidelines apply.

 

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.

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.

Astral Pool is also a reliable name.

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. But there are nuances…

 

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

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

 

Last updated December 20, 2025

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About the Author

Rami Elias Kremesti grew up swimming and fishing in the Mediterranean in Beirut, Lebanon. Water treatment, philosophy and chemistry are in his blood.

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