Plenty of water supplies are drawn from multiple sources and sometimes the mineral content of those supplies differ. Differing water quality can affect the brewing process and beer quality. This is a discussion of how you might monitor and deal with this problem.
The first thing to understand, is if your water supply has the potential to change. A discussion with the water provider can help you understand if the sources change and if the water quality varies. Often, the provider monitors the water quality and can tell you if there is much variation in the water. If it does vary, you need to be ready to test and monitor your incoming water to assess how that will affect that day’s brewing.
There are three relatively simple tests that can be performed quickly and inexpensively in the brewery: Total Dissolved Solids (TDS), Calcium and Magnesium Content, and Alkalinity testing. TDS can be quickly measured using a portable electronic device that is inexpensive and fairly reliable. If the water sources vary between high and low TDS sources, a TDS meter will be a very effective monitoring tool. If there is variation, you should then conduct the following tests.
Calcium, magnesium, and alkalinity tests can be performed fairly accurately using colorimetric (color-changing) test kits. They often have the ability to discern those parameters to 10 ppm or less. That should be sufficient for most brewing use. For professional breweries, high-quality test kits can be obtained from suppliers such as Hach and Lamotte. For homebrewers, test kits intended for Aquarium hobbyists by suppliers such as Salifert can provide sufficient accuracy. In either case, the tests only take a few minutes to perform and the results are immediately available.
With that information, the brewer can revise their water report input to reflect the testing results. With the calcium, magnesium, and alkalinity results, the main components affecting mash and wort pH will be known. The only things not precisely known will be the flavor ion content (Na, SO4, and Cl).
For some waters, the main changes are the calcium, magnesium, and alkalinity and the flavor ions don’t change much. It is OK to assume they are similar to their typical values in that case. If the water source TDS changes drastically, then it may be best to proportionally change all the ion concentrations based on the TDS reading and its relation to the TDS value from your original water report. The supporter’s version of Bru’n Water includes a TDS calculation on the Water Report Input sheet to help the user understand what that value is for their water report.
While dealing with a variable water supply is not easy, it can be accomplished with the relatively simple and inexpensive tools mentioned here!