Couple of weekends ago I stayed in the Painted Desert to photograph the Pronghorn, you need a permit to stay overnight there and the ranger asked if I had water treatment or was carrying water, which I thought was odd because there is no available water that I know of there, so I asked about possible water borne diseases in the area and I was told none known but it was just a precautionary question of anyone staying overnite. Not sure but I would think that minerals in the water might be more of a threat here in the desert high country, like arsenic. I don't know if they work well but I ordered some filter drinking straws for the next trip.
Here is where I checked for info, http://www.cdc.gov/ecoli/, there have been 32 deaths reported in the past year of the 60 some reported cases, so I was concerned