UV water disinfection

When UV disinfection is needed and when it is not

In Cabinet Regulation No. 547 on drinking water, the value for E. coli, intestinal enterococci and coliforms is 0 CFU/100 ml. If a test shows more, we first look for how the bacteria get into the water. In a well the cause is usually leaking ring joints, the cover or surface water; in a borehole it is a damaged borehole head or a flooded caisson.

• If the cause can be removed (cleaning and disinfecting the well, sealing the joints, repairing the borehole head), start with that: well disinfection.
• If the bacteria come back even after that, for example in a shallow well with high groundwater, a UV unit is permanent protection.
• If the water is cloudy or contains iron, there is no point fitting UV on its own: particles shield the bacteria from the light.
• UV does not remove nitrates, iron, smells or chemicals. Those need other equipment.

What water a UV lamp needs

UV light works only if it reaches all the water flowing through the chamber. So the water must be clear and free of deposits.

• Iron and manganese deposit on the quartz sleeve around the lamp and block the light, so you need iron removal before the UV if the test shows them to be elevated.
• Hardness: limescale forms on the warm quartz sleeve, so for very hard water a water softener goes before the UV, or the sleeve is cleaned more often.
• Turbidity and colour: a fine sediment filter goes right before the UV, usually 5 µm.
• The exact requirements for the incoming water are in each unit's manual. We compare them with your test before ordering.

How to choose a UV filter for a private house

A UV unit is chosen by the highest flow the house can draw at one time, not by average consumption. If a shower, the kitchen tap and the washing machine run at once, water passes through the chamber faster and gets a lower dose. Flow is given in l/min or m³/h, and the unit must be rated for that flow with a margin.

• A UV sensor, or at least a lamp indicator, that shows when the radiation has become too weak or the lamp is off.
• The option to add a valve that stops the water if the lamp has gone off.
• Lamp replacement: the lamp's output weakens over time even while it still glows, so it is replaced after the number of operating hours the manufacturer states, usually once a year.

How we install UV disinfection

1. Test We check the microbiology and the parameters that interfere with UV: iron, manganese, hardness, turbidity.
2. Place in the line We put the UV last in the whole-house line, after the sediment filter, the iron removal and the water softener, as close as possible to where the water enters the house network.
3. Electricity The lamp runs continuously, so it needs a permanent socket that nobody switches off.
4. System disinfection UV treats only the water that passes through the chamber. The pipes and the water heater after it are disinfected once, otherwise the bacteria stay there.
5. Follow-up After a few weeks we recommend a repeat microbiological test from the tap: well water testing.

How much UV water disinfection costs

The price of a UV unit depends on the flow it has to treat, the sensor and the safety valve. Installation labour is from €40/h; how many hours it takes depends on whether a sediment filter has to go before the UV and the pipes need altering. If you also need iron removal (from €600) or a water softener (from €600), we put the whole line into one quote.

We name the total price once you have described your water source in the form and attached a test. Other prices: prices.