Real life is funny. Most water is contaminated. The water that doesn’t make you sick is still contaminated. Not becoming sick from it doesn’t mean it isn’t contaminated. Just means your immune system was good enough that didn’t noticed.
As for this game? Perhaps something similar.
FYI:
If you feel compelled to drink water irl outside of a bottle or tap. Make damn certain you boil it for 3-5 minutes or use a filter of some kind. Filters are as cheap as $20US these days. Even walmart carries a variety of camp and faucet filters.