water u drink

Two things here.

First, a new water source shouldn't cause diarrhea unless the water is "funky."  If it's funky, you need to be able to treat it.  This usually means:  (1) be able to bring it to a rolling boil for 2 minutes, (2) treat it with 8 to 16 drops of regular, unscented bleach per gallon, depending on how funky it is, and wait 30 minutes before drinking, (3) or get a good water filter and a couple spare filter elements.

Second, no matter how careful you are, you can always get a bug that causes diarrhea.  So it's a good idea to pick up some Immodium, or cheaper generic aquivalent, at any Target or drug store.  Diarrhea can really dehydrate you quickly, so if it strikes, be sure to drink lots of (good) water.