Drinking water disinfection
Drinking water disinfection means killing or inactivating pathogens in drinking water and in water-carrying systems with permitted substances or methods.
In Germany, the Drinking Water Ordinance sets out which substances are permitted for this, through a list kept by the German Environment Agency. This page explains the methods, the rules and the selection for each application.
Drinking water disinfection: key facts
- Legal basis
- German Drinking Water Ordinance (TrinkwV) of 20 June 2023; it implements EU Drinking Water Directive (EU) 2020/2184
- Permitted substances
- only substances from the list under Section 20 TrinkwV (Section 19(3)), kept by the German Environment Agency (UBA), as of January 2023
- Substances for disinfection
- calcium hypochlorite, chlorine, chlorine dioxide, sodium hypochlorite, ozone; plus UV irradiation as a method
- Not listed for disinfection
- hydrogen peroxide (oxidation only); silver (no longer on the list)
- Technical rules
- DVGW W 224 (chlorine dioxide), W 291 (water supply systems), the W 551 series (drinking water installations), W 294 (UV)
- Legionella
- technical action value of 100 CFU per 100 ml, Annex 3 Part II TrinkwV
- Responsible within the building
- the operator of the water supply system, Section 2 No. 3 TrinkwV
When is disinfection needed?
The water utility supplies drinking water that meets the requirements of the Drinking Water Ordinance. In a building's drinking water installation, in tanks, hoses and mobile systems, disinfection becomes necessary once germs have entered the system or multiplied there. The DVGW names microbial contamination as a trigger, where disinfection can become necessary to protect health.
Typical triggers are an abnormal test result, for example for Legionella, a new installation or repair during which contaminants have entered the system, and stagnation, where water stands in the pipes for a long time. For new installations, the code of practice of the Central Association for Sanitary, Heating and Air Conditioning (ZVSHK) applies: flush first; only add disinfection if flushing does not achieve the required quality.
Continuous disinfection or system disinfection?
Continuous disinfection treats the drinking water itself, usually at the waterworks. It uses substances from the list under Section 20 TrinkwV in the quantities set out there; a residual concentration may remain in the water, for chlorine dioxide at most 0.2 mg/l.
System disinfection treats pipes, tanks, containers or hoses. The disinfection water acts for a period, is then discarded, and the system is flushed before drinking water is drawn again. The rules for this are set out for distribution systems in DVGW W 291 and for drinking water installations in DVGW W 551-3. Both name sodium hypochlorite, hydrogen peroxide and chlorine dioxide as proven chemicals. How this works in practice is shown on the page Flushing and disinfection.
What methods are there?
Chlorine, hypochlorite, chlorine dioxide and ozone disinfect chemically. UV irradiation and thermal disinfection at 70°C or above act physically. The methods differ in whether they can maintain a residual concentration in the pipe network, which by-products form, and where they act: according to the UBA list, UV and ozone are not suitable for maintaining disinfection capacity in the pipe network; chlorine and chlorine dioxide can do this.
The page Methods compared compares all methods by addition rate, residual concentration, by-products and limits.
All pages on drinking water disinfection
Drinking water disinfection by application
Each application has its own rules. The pages show step by step how to proceed.
Terms explained briefly
- Disinfection
- Killing or inactivating pathogens with permitted substances or methods.
- Preservation
- Keeping stored water usable. Silver was formerly permitted only for this, as an exception; today it is no longer on the list under Section 20 TrinkwV.
- System disinfection
- Disinfection of pipes, tanks and containers; the disinfection water is then discarded and the system is flushed.
- Residual concentration
- Amount of disinfectant that remains in the water after treatment; for chlorine dioxide 0.05 to 0.2 mg/l.
- Biofilm
- Slime layer of microorganisms on water-contact surfaces such as pipe and tank walls, in which germs are protected from being flushed out.
- CFU
- Colony forming unit: a measure of the number of viable germs in a water sample.
- Technical action value
- Value at which the operator must act; for Legionella 100 CFU per 100 ml.
- System separation
- Physical separation between the drinking water installation and a connected appliance under DIN EN 1717, for example through an air gap.
Frequently asked questions on drinking water disinfection
How do I disinfect drinking water?
That depends on what is being disinfected. You fill a water tank in a motorhome or boat with a disinfection solution, let it act, empty the tank and refill with fresh water. A building's drinking water installation is flushed after a test result or a repair and, if needed, disinfected by a specialist firm under DVGW W 551-3. The instructions for each application are above.
Which substances are permitted for drinking water disinfection?
The German Environment Agency's list under Section 20 of the Drinking Water Ordinance names calcium hypochlorite, chlorine, chlorine dioxide, sodium hypochlorite and ozone for disinfection, plus UV irradiation. No other substances may be used for disinfection.
Must drinking water in the home be disinfected regularly?
The Drinking Water Ordinance does not require precautionary disinfection. It becomes necessary once germs have entered the system, for example after an abnormal test result, a repair or long stagnation. Regular water exchange at all outlets and the right hot-water temperatures work as prevention.
What is the difference between disinfection and preservation?
Disinfection kills pathogens. Preservation is only meant to keep stored water usable. Silver was formerly permitted solely for preservation as an exception and never replaced disinfection; it no longer appears on the current list under Section 20 TrinkwV.
Who is responsible for the drinking water in a building?
The operator of the water supply system, that is, the business or other holder, as defined in Section 2 No. 3 TrinkwV. In rented buildings, this is usually the landlord. The duties that follow from this are set out on the page Duties under the Drinking Water Ordinance.
What biostream contributes
biostream® GmbH from Sehnde near Hannover has been developing and selling disinfectants based on chlorine dioxide since 2001. biostream® ZERO is a concentrate that the user prepares from two components; it disinfects tanks, hoses, pipes, dispensing systems and dental units. More on the home page and under biostream® ZERO.
Permitted in drinking water. Chlorine dioxide is included in the list of permitted treatment substances and disinfection methods kept by the German Environment Agency (UBA) under Section 20 of the Drinking Water Ordinance (TrinkwV). Its production and use are governed, among others, by DIN EN 12671 and DVGW code of practice W 224; for the disinfection of installations, DVGW W 291 and W 551-3 name chlorine dioxide as a proven chemical.
Sources
- German Drinking Water Ordinance of 20 June 2023 (in German)
- German Environment Agency: list of permitted treatment substances and disinfection methods under Section 20 TrinkwV, as of January 2023 (in German)
- DVGW: disinfection in the drinking water installation (in German)
- DVGW Water Technology Centre: final disinfection with chlorine or chlorine dioxide (2009, in German)
This page does not replace legal advice. The version of the Drinking Water Ordinance in force at any given time is authoritative.
Use biocides safely. Always read the label and product information before use. Material compatibility applies when the recommended dosage and contact time are observed.