is distilled water good to use or table water which might be way too acidic? or maybe tap water left for 24hrs? thanks- clanclan
You want your pH to be between 6.3 and 6.8 ... You can get a good digital pH meter for ~40-50 bucks. I recommend Hanna Instruments pHep family. Cheap and works very nicely. People tend to thing that pH isnt important ... but its not something to let go unoticed. Get a tested and dial in your pH. I use tap water left out so its room temp, and use pH down solution by General Hydroponics to get my desired pH level.
Distilled water /should/ always be pH neutral and has no dissolved solids. Tap water depends on your location and should be tested before use. Sometimes it is high and sometimes it's low. Get a pH meter like Maine said. Otherwise you'll be going into it blind.
Everyone's tap water is different so no way to answer the question generically. Most likely if you filter your tap water you will be just fine. You don't necessarily want to input "neutral" water -- what you want in soil is a pH of 6.4-6.8 for the runoff. So if your runoff is too low then you want to raise the pH of your input water to whatever level will get the runoff in range. FYI distilled water theoretically is a neutral 7.0 pH, but after the water has been distilled it interacts with the air and can become slightly acidic.