Here is a article from Popular Mechanix:

LESSON: RESPECT FOR DANGER
CASE STUDY /// Canyon Missteps
Who: Paul and Karen Stryker, 26-year-old newbie hikers in the Grand Canyon, during the blast-furnace days of June.

What happened: Embarking on a tough overnight hike they estimated at 18 miles (the true distance was 29 miles), the couple carried 6 quarts of water apiece.

Crucial decision: Underestimating the danger. After quickly finishing half their water, the Strykers came across a small pool. They rejected it, Karen later said, BECAUSE TADPOLES WERE SWIMMING IN IT.

What happened next: By nightfall, Paul was ill. The next day, with his condition worsening, they left the trail for what seemed to be a shortcut to safety. Their water gone, Paul became semiconscious and died that afternoon, probably of heatstroke. The next morning, Karen found her way to an emergency phone at Phantom Ranch at the bottom of the canyon. End of article.

My comments:
Note that they rejected water because it had tadpoles in it. I would think that the presence of tadpoles means that the water must be reasonably pollution free. I would still use a water purification method. The water can’t be that bad if something can live in it. I’m interested in what everybody thinks about this. Would you reject a water source because it has tadpoles living in it?

If dying of thirst I wouldn't reject any water. 18 mile hike in severe terrain, shouldn't they have had some equipment? A pot, a match? Some fuel? Drift wood? A shelter from the sun?

I wouldn't reject it just because of tadpoles, I might try to filter and boil the water if I could do so relatively easily. The problem they had was the heat of the "blast-furnace days of June". If I were dying of thirst I would not give a second thought to drinking out of a mud hole inhabited by pollywog's.

smitty

I would have filtered the water through a bandanna then boiled it and had plenty to drink.
In this case I would assume the water was not too bad since it was obviously able to sustain life.
Some water is better than no water.

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).

Why not! Heck, most of the world drinks raw pond water.

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.

I´d think twice before I drank that water without means of purifying it. Even without industrial pollution it may be pretty bad. A hot summer day means that the water was pretty warm too. In warm water bacteria and algae grow fast. As that´s what tadpoles feed on there where some for sure. Some algae produce poisons that can make you throw up. So drinking that pond water could promote dehydration.
Tadpoles are not an indicator for unpolluted clean water.

Ironic, we have several running posts about the climbers dying from hypothermia up on Mount Hood and now somebody of heat exaustion down in the Canyon. I suppose the answer lies in remaining safe on the flatlands where smiling bobbleheads give us timely warnings about rocking chair recalls followed by a coke commercial- a substance no tadpole can survive in. The answer to this one is easy. Quoting Edward Abbey about desert travel, " Carry lots of water. Stay out of the noonday sun. Pray frequently." <img src="/images/graemlins/grin.gif" alt="" />

Hmmmm......

The Darwin Tadpole Filter method of cleansing the gene pool.

Sue