Reverse Osmosis....

We have a Spectra Pure one. Have had it for years. I used there equipment when I was playing with salt water swim tanks and liked the quality of it. Recently replaced the filters and the membrane. Membrane is a "90 gallon a day" piece. Have spoken with Spectra Pure about how they come up with this number. It is at a certain pressure, don't remember the psi. Water temperature of 77*. I checked our water temperature today...57*. This was after I had a hydrant open and free flowing for a few minutes. I had my hand on the hydrant, felt the pump come on....so I know I was measuring water directly from the aquifer.
Any suggestions on how to warm the water up to 77*?