Distilled Water?

[TinGoat]

I suppose that it depends on the quality of your tap water.

Hard water with a lot of minerals will effect the quality of the paint job.

Chlorines and Flourines may also effect the paint, but they will settle or off-gas if you let the water sit overnight...

Pure distilled water is only ~$1.50CAD for 4-litres, and it makes a better cup of tea or coffee than tap water.

Another way around the subject is to filter the water. Use a fresh "Brita" filter or reverse osmosis filter on your domestic supply.