This is America. Our toilets use _clean potable water_ to flush our shit.

Drinking water from the mains is metered, so it is observable from the business perspective. Life finds a way. Heat exchangers and datacenter plumbing absolutely breed life and put things into the water that were not there when it was pumped in.

Imagine if a datacenter used a shady supplier of pipe that used, say, lead in their alloy. Do you want that datacenter grey water going into crops?

The water from the lake isn't drinking water either, it is contaminated with all sort of stuff including dead animals and animals excrements. But it doesn't mean it is not suitable for agriculture.