I've been using water from my garden hose ever since I put my system together 3+ years ago, and I don't have any filtration system. I did have an issue with a small solenoid jamming up from some corrosion buildup - not rust, just gunk. Aside from that, tap water has been working fine and I continue to use it. Go distilled to minimize crud buildup. In any case, its wise to break the system down and check for crud at the beginning of each season. Hope this helps.