Where to get the water from, look for ideas.

You can get the standpipe from the municipal utility, you must leave a deposit and upon return, the rental fee plus the consumed amount of water will be deducted. Find out where the nearest water connection is. If it's on a busy road, you have to be careful, the standpipe must be secured according to [STVO]. If someone hits it, you’ll have a huge problem. However, the standpipe usually remains set up only for the cleaners and screed layers over a longer period.

You can get 30-liter canisters from the heating and sanitary technicians. They have plenty of [Solarflussigkeit].

Since you mentioned rain in another post - also a method to get water: set out buckets and collect rainwater :)

Regards