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The supply hose should have a 3/4” inside diameter (ID) and be no longer than 50 feet. 2. The water supply pressure must be a minimum of 20 pounds per square inch (PSI) and a maximum of 125 PSI. The flow rate must be at least 3 gallons per minute (GPM). 3. Use a water softener if there is high mineral content in the water of your area. High mineral content causes excessive scale build-up in the coil/heat exchanger. 4. Un-roll the hose reel and then connect one end of the high pressure discharge