You need a standard to keep things consistant. I live in Central Texas where the summers are very hot. Tap water is way above 68 (F) this time of year. As mentioned above I keep a jug of water in the fridge and pour some into my gallon of "to be" 68 water along with the warmer tap water. a bit of adjustment here or there and I have my 68 degree water, All my Chems are mixed and all my rinsing is done from that jug.