Some people use distilled water, others don't. It really depends on the quality of water in your area... do you have a PPM meter? If not, it's a good thing to get from the hydro store. They aren't cheap but it measures how many parts per million are in the water. If your tap water is over 400, it's probably time to use distilled water instead. If not, you are fine. The PPM meter also helps you to know how much of your nutes you added to the water. Pretty handy tool