What do you mean by quality? Are you planning on using gray water? Be aware that plants do uptake impurities, and many retain them to the point of harvest. Heavy metal content should be a concern as well as some biological concerns. Untreated sewage should never be used. Pesticide/herbicide runoff and fertilizer salts can also be problematic.
In my limited experience with a hydoponic 'dripper' type system thingy, the pH of the water does matter. Up here we have 'soft' water so I was ok, but if you had hard water there was an addidive you could buy and add. It also effects the ammount of nutrient you should be adding as it will give a different reading! Something like that...
