PH dropping when adding Neutral water.

Yeah, make sure you use distilled water to calibrate you PH meter. Tap, spring, or any other water source will always have varying PH levels, so likely the water you are adding is just more acidic, or your PH tester is off. The good news is that you are probably overthinking it. More likely than not, your standard tap water will be alright if you let it sit for 24 hours to get rid of any chlorine. You should only have to augment PH if you experience invest nutrient lock, and you can do so simply with lemon juice or aglime (one goes up, one goes down)