Secondary Homes and Drinking Water

Stagnant water in drinking water pipes occurs whenever a pipe or part of a pipe remains unused for an extended period. An effect can appear within just a few hours, but after a week, it’s advisable not to drink the water directly from the tap; instead, let it run for a moment.

Vacation homes and secondary residences are particularly affected due to their irregular usage.

What is stagnant water?

Water that doesn’t move for more than 4 hours is already considered stagnant water. Typically, it only becomes a problem after a few days. This can happen in dead ends of water pipes, storage tanks, or rarely used parts of the installation, such as when water remains unused for a long time in secondary residences.

Frost-proof valves are often installed on outdoor taps to avoid emptying the pipes in winter. These sections then remain inactive during winter but still connect to the home installation.

If the water exchange isn’t maintained for an extended period, a biofilm can develop on surfaces. This layer consists of bacteria and sometimes algae.

What problems can arise from this?

Stagnant water provides an ideal environment for bacteria

Stagnant water pipes, especially at elevated temperatures, provide an ideal environment for bacteria. If these pipes already have a layer of lime or corrosion, this creates an even better growth medium for bacteria cultures.

Bacteria from long-standing sections of the system, such as the pipes leading to outdoor taps, can quickly spread back into the main system, where they can multiply further.

The risk of Legionella is especially notable here. These bacteria can thrive in stagnant, moderately warm water (between 20 and 55°C), if present.

In cold water pipes, where the temperature should be below 20°C, bacteria generally don’t multiply quickly. However, in secondary homes, the extended period of stagnation promotes bacterial growth. The presence of a biofilm also encourages bacterial spread.

Cold water pipes are sometimes installed near poorly insulated hot water pipes or loop systems, resulting in an unfavorable water temperature (too high to prevent bacteria growth but not high enough to kill them).

Heavy metals and other substances enter the water

In older pipes, there may still be lead or other toxic substances. This is a common issue, especially in older secondary residences.

When water flow is poor, these heavy metals and other substances can dissolve into the water and concentrate.

What can be done about it?

Upon arrival at the residence, it’s advisable to set the hot water boiler to a sufficient temperature (above 65°C, ideally 70°C) and wait before taking a hot shower. Legionella can enter the body through the lungs, often via aerosols generated while showering.

The pipes should also be thoroughly flushed upon arrival before use.

It may also be helpful to completely drain the water during extended absences if possible and if the installation is designed for it.

A water analysis can provide insight into the condition of the installation, and regular analyses are recommended. The frequency of such analyses depends on the age of the installation, frequency of use, and other factors. Our team can assist in planning.

Another option for worry-free water use is the installation of an appropriate water filter. This removes most germs and heavy metals without removing minerals from the water.