My best suggestion to you mate jsut so happens to be, use bloody tap water, and let it sit out for a small while. THat, or you could just simply touch each section, filtered tap + rain water. It the rain's pH is mostly acidic, and your tap is mostly alkaline, then, combine both, let it stand for a few days, and voila. (Might be a good idea to boil it to make sure it's sterilised some, otherwise, you wouldn't want a microbial infection of your plants.)