I grew up in the high deserts of southern California. The neighborhood where I lived was an older open community development (the big community developments today are closed, with brick or privacy fencing) that took up a 1.5X0.8 mile rectangle. Because the area was flat the developers, when building/planning, were able to grade the whole community enough so that any excess water in the yards (back and front) would drain to the street. All the streets were graded with the natural dip of the valley, south to north and west to east.

When the waste water got to the north side of the community it hit an east/west street that was graded to push the water towards the four through streets in the community, there were then 'dips' in the east/west road that were graded to move the water across the main street and north out into the desert into open drainage ditches that took the waste water a quarter mile into the desert before the water disappeared.. looking back on it I believe it disappeared into an irrigation type of drain buried in the desert that then took it by pipes to the water treatment plant less then an eight of a mile beyond that (Thats the only reason I can place to the many manhole covers out in the middle of the desert).
No matter the severity of the drought or time of year, there was always water in these ditches.

There were tadpoles in the open drainage ditches.

Understand that the water that was collected into these open drainage ditches was run off of everyone's properties so there were pesticides, fertilizers, oils, gas, antifreeze, paint and paint thinner, soap, and whatever else people carelessly let run down their driveway or put on their yards.

My point is, with all the chemicals I know were in the water, it was still water that "...something can live in...", including tadpoles.
I would never want to consider drinking from that water without some sort of filtration that would remove all those chemicals, however in the situation that you described, I might have taken some of the water I just described and chanced it if I had to.

However, having grown up in the desert, if I was hiking and wasn't at the place I was going to camp, or refill at by the time a bit over half my water was gone, I'd have been turning back. But then I also pretty much knew how much water I needed to stay out, active, all day in 110 degree heat with 7%-0.7% humidity with no cloud cover or chance of shade.

Where I live now on the other hand its hard for me to tell how much water I need when its 90 degrees 90% humidity and overcast.. I seem to need more, and live in a state of very slight perpetual dehydration during the summer months.. and my body does not seem to whisper to me 'you need water' here as it did in the desert (I'm just not as thirsty).