It is critical to match the reverse osmosis membrane with a correctly sized drain line flow restrictor to ensure the proper waste-to-product ratio is met. A mismatched combination will allow either excess water to flow to the drain or cause premature fouling of the membrane. The waste-to-product ratio may vary slightly from one manufacturer to another. The chart below provides you with the standard ratios used. The first number (3) indicates the waste and the second number (1) indicates the portion of purified water produced during the same given time period. REMEMBER that the reverse osmosis system comes with a shut-off valve that stops the unit from producing any waste or product water once the reverse osmosis storage tank is full. The average household reverse osmosis system will waste less than 2 flushes of a toilet.