So, what are you supposed to do with free ranging chickens? Spend your days chasing them off from every water source that didn't come from a faucet? This kind of veers off into left field for me. Animals DO drink from natural water sources, it IS normal, and they stay healthy in spite of it. Let's remember that chickens are domesticated wildlife -- jungle fowl aren't watered from a filtered water source. If it's parasites you worry about, water is less of an issue than dirt and other animals.
If providing filtered water works well for your set up, great. But let's not imply that people who let their chickens or pets drink from a natural water source are doing it wrong, or worse, being irresponsible.