Water quality

Contaminants in the water supply are not responsible for as many problems as is usually assumed – in Germany in particular, tap water is of high quality. Although most tap water contains some impurities, most of them have no photographic effect. Therefore, the use of distilled water, as sometimes recommended, is not necessary for the preparation of working solutions.
At most, large amounts of suspended organic matter, particles of finely divided sulfur, hydrogen sulfide, and soluble metal sulfides would be the only impurities that could cause serious problems for the developer.
Extremely hard water can produce a finely divided precipitate when the developer is mixed. This can produce a sediment, but even if the particles remain in suspension, they will have no photographic effect.
Certain developers that are clear when mixed may form a finely divided precipitate after use. This is a normal effect and is not an indication of poor mixing or impure water.