Take PC's advice and test with nutrients. Do everything you can to not have to carry water. Don't forget you are supposed to flush your system every 3 or 4 weeks and start fresh... more water carrying. Even if your PH climbs, depending on how much and how fast, you might want to consider letting it climb and adjusting it from time to time in the resevior. Much better than hauling water.

I have the parts, but have yet to build an automatic PH doser. You may want to consider something like this, that way you don't have to ever worry about PH, except in the beggining when you are figuring out amounts. If the PH gets too high, it automatically injects PH Down into your system. Using this, I don't think it would matter much if the PH in your tap water rises. I know mine does. I adjust it, and grow big beautiful buds.