We always suggest filling your tanks with water from a clean, trusted source. Generally, the city water that comes from your tap is a good option. If your water is coming from wells, rainwater, and other outside sources, it is important to make sure your water is treated and filtered before storing it. Proper treating of your water, along with using a water safe hose will help prevent growth of bacteria, algae, mold, mildew, and other contaminants. See below links to our filters and our water safe hose. High volume filter Low volume filter Water safe hose