PH water & add nutes before pouring it in.. You'll get a feel for how much your nutes affect PH with a little practice. Also, dont use Any nutes at all until the plant is 2 weeks old, then start at about 25% of what is directed on the label. So at the very beginning, your only testing/balancing the PH, and making sure your water is clean (low PPM). Usually Well water, or city water with additives, will already have crap in it you dont want. This is why you see people using r/o (reverse osmosis), rain, or purified water.. Don't worry about testing the runoff until the plants are bigger.