The main characteristic to look for in lab water is consistency. You will have no problems if the water with which you make your development run is EXACTLY the same as the water you used to do your initial testing. Almost no matter what kind of crud it contains.
What screws things up is water which is unpredictably changing in some way: alkalinity, iron content, or of course temperature.
Here in New England, the autumn leaves fall into the reservoir and decompose. Then the winter road salt washes into it. Then one week the boys at the purification plant get a little carried away with the chlorine. The next week, the city chemist is on vacation and nothing gets added.
Thus the need for some sort of bottled water...