Properly dimension drinking water pipes.

I used complete aluminum composite pipe. I hardly believe that plastic pipe is cheaper. I paid 48 cents per meter of pipe. For 20mm pipe 80 cents per pipe.

§ 12 (2) of the AVB-WasserV, the installation and significant modifications may only be carried out by installer companies that are registered in the installer directory of a WVU. ...

If the cross-section is too small, the pressure loss is too high.
If the cross-section is too large, the retention time is too long.

Damages to buildings are "only" monetary damages.
The risk today exists especially with the simultaneous use of rainwater.
Due to excessive enthusiasm or a desire to save money, for example, pathogens can enter the own system and the public network through faulty installation.
To prevent this, many municipalities or utility companies want only specialists to handle the installation of water pipes.

so sizing a water pipe is not that difficult.

the flow velocity in the house should be about 2m/s (or less). with the pipe inner diameter you can now calculate the cross-sectional area and immediately know how much water will reasonably flow through in time x.

now you "only" need to know how much water each individual consumer uses and you can already size it.
if the branch lines are very long, you should preferably size a bit larger. however, with a circulation line there are no long branch lines (10m and more). now you have to add up all the consumers in the house that will reasonably run simultaneously and can calculate the pipe diameter for the circulation.

e.g.:
could run simultaneously:

showers bathroom 1 20l/min
showers bathroom 2 15l/min
bathroom 1 washbasin 5l/min
washing machine 10l/min (because it is just starting)
dishwasher 10l/min

also present:
bathroom 2 washbasin 5l/min
kitchen sink 5l/min
outside tap 20l/min

total amount theoretical: 80l/min
calculated theoretical highest necessary consumption: 50l/min

50l/min= 3m³/h

DN20 pipe at v=2m/s 2.3m³/h
DN25 pipe at v=2m/s 3.6m³/h

selection: DN25

the values above are purely fictional. the real consumptions are often indicated on the devices and naturally also depend somewhat on the water pressure. you should seriously consider which consumers will run simultaneously. the above example is not so great, because you don’t have to keep a bigger pipe ready permanently for 5 washes per week. but if you wash in the morning while showering, that is unavoidable again. you should definitely avoid undersizing, otherwise the typical old building gurgling starts...

i would worry much more about making sure the thing is watertight in the end.

§ 12 (2) of the AVB-WasserV, the installation and significant changes may only be carried out by installation companies that are registered in the installer directory of a WVU.

As said, no plaintiff, no judge

Morning Morning

THANK YOU

Take a look at an aluminum composite pipe. Often also called PEX. Anyone can do it themselves with that. Just use a few compression fittings. Holds great.

Hi Nelly

That is really nonsense




Olli

The regulation is different for every water supplier. Not everyone has this clause included that only installers are allowed to do it.

The idea that anyone can do a complete installation is nonsense. Such a sensitive topic (tightness!) definitely goes wrong so easily without basic knowledge.

However, every trade also tries to create a certain magic/barrier through half-truths so that the stupid customers don’t do it themselves and one can’t make money from it. Because mounting a new faucet once costs quickly 150€ including travel, etc., without material costs. Completely improper and virtually usury. If I ask a plumber friend, it either costs a few bottles of beer or 20-30€ for basically the same service.