I use water in my modded ECB and only have control problems when it runs dry. With a full pan I can hold 250 for 4-5 hours, when it goes dry it'll hit 500-550 within 10 mins. I use hot water from the sink faucet and add about 2 qts of boiling water that I made on the stove and no probs. As far as too much water, ain't no such thing. It'll evaporate at the rate that it evaporates at, you may just have to add some once in a while if doing a long smoke.
The early bird may get the worm, but the second mouse gets the cheese.