24.5C 25.5C (78) here
http://www.wbuf.noaa.gov/tempfc.htm
Heater is my controller and water tubing coil cooled with cold tap water is my chiller.
I run a 1/4 inch OD tube from my RO/DI inlet to the sump, and back to the P-trap, with straight valve slightly open to the fast drip.
There is a 15 feet tube coil in the sump acts as a heat exchanger/cooler.
Back to the RO/DI waste line and in to the drain. water cost for a few short Summer month in Vancouver where it rains 9 month out of 12 is nothing compare to the cost of the controller and chiller and electricity to run the chiller.
Cut water supply line to RO/DI and insert the 1/4" OD line in with straight line valve for flow control.
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Run the tube line to you sump and make a coil that will act as a heat exchanger
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Run the tube line back to the RO/DI waiste line and or back to the P trap
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You summer chiller is on line !
If water will get below set your heater will kick in.