Good evap means good kalk usage. Nice to hear that the heat isn't a big problem even in AZ.I have a couple little fans that blow across the top of the tank. I live in AZ and even in the summer they keep the tank water below 78 degrees. Unless you have a house that doesn't have AC, or keep it really warm, you'll be OK. Evaporation (via the fans) and a good top off system will take care of it.