try to find a distilled reverse osmosis water machine around your neighborhood. theyre fairly common around groceries stores and what not.
fill up a 5 gal container if you have to.
im lucky enough to know a girl who has a PH water machine and can make water at whatever PH it needs to be (some organic life water crap or something).
flushing with tap water is really the easiest, most practical way to do it (bathub) so it makes it hard to control the PH.
like suggested earlier, its probably safe to flush with tap, let it dry out, then supplement with low PH waterings, 5-6.5 if possible, even in soil.
my PH readings in soil are at a mild to high 7.5, which is way too high, but im also using a really cheap 5$ PH meter. i constantly flush with lower PH water to assure the PH doesnt rise too high!