In the middle of the desert, on a hot summer day, I would drink it. Especially if I had miles to go and there was no more water left with me.

I'd rather chance "beaver fever" than die on some dusty trail because of tadpoles in the water. (Heck, might as well eat the tadpoles, too... protein.) I'd try to filter the water as best as possible with a t-shirt, assuming no other water purification means.