30-second rule

"During normal operation, the temperature of the cold drinking water must not exceed 25 °C for more than 30 seconds after a tapping point has been fully opened and the temperature of the hot drinking water must reach at least 55 °C."

DIN 1988-200, 3.8 Operating temperature

As cold and hot water pipes are often laid in installation shafts with circulation and heating pipes, the water temperatures equalise quite quickly during downtimes. In the event of an inspection, this rule is checked on the basis of temperature tap profiles at the respective taps. It is of great importance in current legal disputes regarding contamination, especially in cold drinking water installations.

If the aforementioned rules are observed, the drinking water installation can most likely be operated in accordance with the generally recognised rules of technology. If this is not the case, a planning/execution error can be assumed.

Note:

In cold drinking water installations, it is therefore essential to check compliance with this rule during the planning stage.

This is not necessary for hot drinking water installations. Here, the 3-litre rule, which is a stricter requirement, is checked as standard in a calculation with CALHYDRA. If the 3-litre rule is adhered to, the 30-second rule is also automatically fulfilled.

Figure 1. Temperature tap profile on a tapping valve for cold drinking water

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