I wanted to elaborate a little on how anaerobic technologies could be used to alleviate the water shortages in many parts of the world.
Basically in most waste water treatment plants the water is mostly treated aerobically. This is analogous to an aquarium with a large bioball filter. It creates water with a lot of nitrates but the water we drink can only have up to 10 ppm of nitrates so most of this treated waste water is used as "gray" water to water lawns or irrigate crops. A lot of it is also just dumped into rivers or other waterways or allowed just to seep back into the water table though. This creates water pollution in many lakes, rivers, and streams. For example, at the mouth of the Mississippi river there is a 7000 square MILE dead zone (bigger than the state of Rhode Island) and the sole cause of it is nitrate pollution in this area. I am originally fron the state of Louisiana and the entire Atchafalaya basin (a HUGE swamp like area) is basically a dying ecosystem solely due to nitrate pollution.
So the most common way to treat wastewater is with something analogous to a water change except that a lot of the discarded water winds up polluting our lakes, rivers, streams, and even oceans. I believe a lot of the earths coral are dying due to nitrate pollution as well.
This causes water shortages because the replacement water comes from the water table. In many areas of the world and in the US there is simply too much water being taken from the water table too fast.
If anaerobic processes were the standard to treat ALL wastewater then water pollution would decrease tremendously and possibly cease to exist altogether (anaerobic processes are used to remove all sorts of nasty chemcals from the water.) See May 2001: Anaerobic wastewater treatment reviewed
Also, there would be much less water that would need to be drawn from the water table for municiple needs. There would still be plenty that could be diverted for agricultural needs in most areas. This type of large scale anaerobic plant could also produce biogas which would offset any additional cost of such a plant.
All I am saying is that there are solutions or compromises to most problems and being open to new and improved ideas are key to getting there.