There is a reason that water was one of three things included in Reinheitsgebot, the German law of 1516 that governed the purity of beer.

The reason? It’s important.

It can make enough of a difference that when the same beer is brewed in two locations — like, say, Southern Tier’s now discontinued porter from the mothership brewery in New York and the locally brewed version made on the North Shore a few weeks back — the difference in the water can make it seem like you’re drinking two different beers.

Southern Tier’s Cassandra Buncie and Justin Schau help explain: