UV-C ultraviolet disinfection: what it offers your pool

What the UV-C lamp does in the circuit

The unit is a chamber fitted on the return line, after the filter. Inside it is a UV-C (type C ultraviolet) lamp, protected by a quartz sleeve. The water flows around the lamp and receives radiation that destroys the genetic material of bacteria, viruses and protozoa, so they cannot multiply.

There is a reason it goes after the filter: the radiation only works well in clear water, because particles “shade” the germs. A correctly sized, clean filter is a precondition for UV to perform.

Germs and chloramines: what you gain

• An extra barrier against resistant germs. Some parasites, such as Cryptosporidium, survive in chlorine for a long time but are sensitive to UV-C.
• Fewer chloramines. The radiation helps break down the compounds that chlorine forms with sweat and urine, which cause the heavy “chlorine” smell and red eyes.
• Lower chlorine consumption. Since part of the disinfection happens in the chamber, chlorine can usually stay towards the lower end of the 1–3 mg/l range.
• No added chemical. UV leaves nothing in the water and does not change the pH.

Why you still need residual chlorine

UV acts only at the moment the water passes through the chamber. Once it is back in the pool, it has no protection at all. Every swimmer, every leaf and every bit of dust brings in new germs, which stay in the water until they pass the lamp again. In the meantime they can multiply or start algae on the walls, in spots the circulation struggles to reach.

That is why UV is considered a supplementary method. Free chlorine stays in the water as a residual disinfectant and covers the whole pool, all the time. UV simply leaves it less work to do.

There are also things UV does not do at all. It does not clear cloudy water, it does not correct pH or alkalinity and it does not remove algae already stuck to the liner. These still call for proper filtration, regular testing and brushing, as in any pool.

Installation and maintenance

• The unit is sized to the pump's flow rate. If the water passes through too quickly, it does not receive enough radiation.
• It only works when the pump is running, so pump running hours matter here too.
• The lamp gradually loses output even if it still lights up normally, and is replaced at the interval the manufacturer specifies.
• The quartz sleeve needs cleaning of scale, especially in hard water.
• Never look at the lamp while it is on, and never switch it on outside the chamber.

Who it is worth it for

UV makes sense for families with children or people sensitive to chlorine, for pools in frequent use, and at guest accommodation as an extra barrier. For shared-use pools, the engineer and the competent authority confirm what disinfection is required; see also the rules for pools at tourist accommodation. We check at the site survey whether it fits in your plant room and which unit suits your pump.

Questions

See also