Depending on where in he world you are, and how bad tap water it is where you live, if you can drink tap water, you can use it as enema too.
If tap water have a lot of chlorine, leaving it to stay in clean glass bottles for a few days will help with chlorine.
Using some cheap countertop filter could help with other impurities.
Boiling water can help with removing chlorine, but if you are boiling water inside chrome-nickel stainless steel pot, that water will take some of the chrome-nickel in, that is why just keeping it stored inside glass bottles could be a better idea.
Anyway, whatever water you are not afraid to drink, that water you can use as enema water.