Originally Posted by ajdelange
If this results in wildly fluctuating water parameters then that can be a problem to which the solution is either self analysis of the water each time brewing is contemplated. While this is not difficult to do it adds more work to the brew day and the test kits do cost some money. The other solution is to remove the variability by removing the minerals and replacing them with your own i.e. by using RO water. While there is still the nuisance of having to add the minerals at least they are the same mineral each time (per style). OTOH if all the sources are similar to the 2 reports that have been posted here the water is pretty mineral free and the variations would, therefore, be small.
You are absolutely correct. Having looked at the water reports from all of the different treatment facilities, there does not to seem to be drastic fluctuations among the different sites.
However, I am a total OCD control freak and started using RO six months ago.