The municipal water source where I live is Hetch Hetchy, the same as in San Francisco, and is an extremely good tap water source. I've used it for years to mix 5L batches of Xtol. However I have noticed a black stringy growth in the unused developer at around 6 months storage in a floating lid container - I usually finish off the 5L well before 6 months. Because of that I switched to steam distilled water and never saw that again even recently with small quality of remaining developer at 7 months out. You can buy steam distilled water at Walmart for 80 cents a gallon.

Thomas