Sanitary warranty 5 or 2 years for self-contracting?

Dear forum members,

Short: In the case of a house connection as part of a new build with self-provision of the sanitary service, is the warranty 2 years or 5 years?
In the specific case, the piece of pipe where the valve for the house connection is located is cracked (behind the water meter, so the house system, not the water utility).

Long version:

Last year, during the meter reading, we already noticed that there was water standing in the shaft. BWB people said that this was normal when it rains a lot (which it did last year) and that this actually does no harm to the installation, only for reading the meter next year it would be better if we pumped it out once.

Now, with the hot days and little rain, we thought we would pump it out. The neighbor had already pumped for several hours yesterday and today discovered that the shaft was full again. So we pumped it out again, and when the water level slowly reached just above the installation, you could already see that there was a current, specifically at my piping. We pumped further and first closed the valve in front of the meter. When the water level dropped slightly below the installation, we slightly opened it again. Then you could see that a jet was shooting out at the piece of pipe where the valve behind the meter is attached. Upon closer inspection, you could see a fine crack running through the entire threaded coupling.
Now the question would be whether this is still under warranty?

It does not matter how you commissioned the company. What counts is whether the installation is considered "permanently attached to the building." In this case, the warranty is 5 years.

Just learned from the plumber and [Wasserbetriebe] that up to the first valve after the meter, [Wasserbetriebe] are also exactly responsible. Lucky break.

You can still help me if you have experience with this. How do you handle the excess consumption? Do you base it on the difference to the previous year's consumption or an average consumption? The meter shows 235 m³ after not quite a year. Last year we had 112 m³. I would say that excess consumption due to the defective valve plays a role.

Is this based on the difference compared to previous years' consumption or an average consumption? The meter shows 235 m³ after just under a year. Last year we had 112 m³.

The difference consideration compared to previous years' consumption is a very good estimate - as long as family circumstances have not changed drastically.
The order of magnitude is not surprising; that's about one Kölsch glass per minute. A barely audible running toilet flush uses more.