Does water temperature matter?

Never use hot or warm water.  Water coming from your water heater is laden with metals (check the bottom of your water heater sometime to see what has accumulated), and water over 110F will ruin a membrane in minutes.  Always use the cold water line.

The ideal temperature is 76° F and yields the best results.  During the winter months, source water comes out of the pipes much colder.  If the water is 50° F, the gallons per day rating of a system will be cut in half. That means a 100gpd system will produce 50gpd instead because the colder water is harder for the membrane to process.