Maybe we need to ask the OP how much water he thinks he has to use per print process?
If he uses 100 liters per print, it'd boil down to €0.30 to €0.60 per print. That's a LOT of money to waste on water
and I don't really see how you'd manage to dump THAT much water down the drain for a single print to begin with, but it'll be in the ballpark of the same amount you spend on silver, maybe a little gold chloride for toning (actually that would bump you way beyond this figure), etc.
I just received our water bill and we're by no means economic with water, and there's of course my darkroom that's used fairly frequently. Our total water use was 93m3 (93,000 liters, ca. 25,000 gallons) - this includes all my printing for the year, not to mention watering the backyard on hot days, occasionally washing the car - and the main consumers: showering & flushing toilets. We're still below the national average per capita with this. I'm saying this because I have a hard time seeing how you're going to run into financial trouble due to water use in a domestic darkroom printing operation. I wonder if it's even possible in the first place.
Orders of magnitude and all that.