Originally Posted by Rain Man
I apparently don't understand water filtering.
So I turn on my water tap. In my case, that water started out on top of a mountain, and then it flowed down and went into a reservoir. Then it flowed down a big rock tunnel to Denver, went through a bunch of pipes, and via some sort of magic it comes out of my sink.
At some point in that process, that water got treated, right? Someone had to filter the water bugs out of it and the giardia and stuff. Are there things that a filter can't get out? Or is the problem figuring out what to do with the stuff that gets filtered out?
I've seen simple filtering systems in survival kits that are basically a plastic tent. You let the water evaporate inside it, and it recondenses in the heat on the tent. Then it drips down and you drink it. The stuff that recondenses is presumably two parts hydrogen and one part oxygen. It contains no water bugs or giardia or fracking solutions, and the filtering costs nothing.
Denver has 30 MGD (millions of gallons per day) of recycled water treatment capacity (soon to be increased to 45 MGD). It treats water from one of your sewage treatment plants and dumps it into your drinking water reservoirs. Denver wouldn't resort to recycling water unless the water demand of the city did not exceed what can be provided by those mountain streams. Sounds like Denver is in a water stressed area.
Denver has three other convention drinking water treatment plants that treats river water. Each of those plants are between 250 to 300 MGD. So somewhere around 3% of Denver's water is currently recycled. You can read about the conventional treatment process here:
This process is designed to move turbidity (particles that make the water cloudy, probably very little from those mountain streams) and microorganisms. It won't remove salts and dissolved organics that might be part of fracking fluids. The fracking fluids can be removed from water, but it might make the water 4 or more time expensive to treat.
Your tent style water purification system requires distillation. For the little amount of water that is required for a camper or two, solar energy can provide the needed energy. To distill 900 MGD or so would require a tremendous amount of energy and be prohibitively expensive.
Your statement about the earth being a closed system with respect to water is correct. But it is a matter of the amount of fresh water available at a given location. Of the total amount of water in the world only ~0.007% of it is in lakes and streams and ground water supplies that are easily accessible for human use. Growing population, the lack of water where people live, and increasing pollution levels, and changing precipitation patterns due to climate change all put additional stress on water supplies. It's a monumental problem on a global scale.