Attach this filter to your hose when filling your spa or hot tub with fresh water to reduce all impurities in your water, including but not limited to: iron, lead, scale and other heavy metals. This is an absolute must for well water users! It will also eliminate chloramines, hydrogen sulfide as well organics that cause odor. By using a pre-filter, you will reduce the amount of sanitizer needed. This pre-filter is good for 2-3 fills, and numerous top-offs. Use it once and instantaneously see your water clarity improve.