There must be 50 - 100 analysis a lab can run on water to test for bacteria, minerals and toxicity etc. At between $8 and $100 per analysis, I am assuming you only analysed the basic parameters. When samples are collected, they must be placed in an esky with dry ice or ice at a minimum. For pH, the samples need to be in the lab in under 6 hours, for other analysis, 24 - 48 hrs. This probably explains running pH test yourself. Did you use a callabrated probe or paper strips? Paper strips only record whole pH points, so at best you can be 0.5 pH points out but probably closer to 1 pH point. Did you sent QA forms with the samples. There is more importance on collecting and storing than running tests. When you say perfect, what does this mean?? Perfect would be deionised, but little would live in or on it? Dont flame too hard, I test water quality (environmental rater than drinking) for a living,,, its my thang!!
Not sure about this, but I would quess that some people out there have produced homebrew without sanitising correctly, possibly for 10 years or more without lost batches. Why spend time sanitising then use water with unknown chemical and biological parameters. For me it is all about eliminating variables and unknowns. In saying that, I only use filtered tap water which may pick up solids, maybe some bacteria or the odd stray cation (+ charged) but does little to pick up anions (- charged, chlorine, flouride etc). The thing with tap water is test are constantly run at the treatment facility so it takes a bit to become contaminated and really unlikely to happen (without everyone hearing about it anyway).
Good luck with the tankwater, I hope you can all keep slipping your batches through to the keeper, not sure how they arnt bing hit for a biological 6 and out..