In a typical RWH system, rain falls on the roof, runs off, is captured in gutters, and flows to a storage tank, rain barrel, or cistern. The storage tank acts as a mini reservoir. A filter can be installed on the inlet side to divert contaminants that may wash off the roof, allowing mostly clean water into the tank. Rainwater can be stored above or below ground. Once the tank’s capacity is exceeded, water is diverted through an overflow near the top of the tank. Overflow can be channeled into a bioretention area such as a rain garden or swale. Stored rainwater can be used indoors for nonpotable water use (such as toilet flushing) or outdoors for irrigation, car washing, or filling water gardens or birdbaths. This reduces the demand on potable water supplies. Runoff reduction benefits occur because the volume of water used is eliminated from site runoff. When water supply needs are reduced, so are water withdrawals, which increases baseflow to streamflows.