All RO membranes are subject to three things; your water quality, water pressure and water temperature. The membrane is rated at 77 degrees and 50 PSI. For every pound of pressure lower than 50(PSI) subtract 2% of the output. For every degree(F) below 77, subtract 1.4%. Example 1: Let's take 40 PSI water at the 77 degree temperature with a 50 GPD membrane. 50 GPD - 20% (40 PSI) = 40 GPD. Example 2. Now let's take the 50 PSI, but reduce the temperature to about 40 degrees: 50 GPD - 51.8% (since it's 37 degrees colder x 1.4) = about 26 GPD Note that the typical waste water ratio is about 3 to one in a 77 degree and 50 PSI environment. So in a 50 GPD membrane you will waste 150 gallons of water to make 50 gallons of water. Lower tempurature and PSI will INCREASE the waste water, So in the above examples the total water will remain at about 200 gallons so the waste water will be 160 in example 1 and about 174 in example 2. These are all estimates but you get the idea.