[Atomic-S (OP)]

Southern Arizona has long enjoyed hard but excellent water from local aquifers, but the supply hs been overpumped for many years. This situation started creating problems, which finally were solved, for the time being, by the constrouction of the Central Arizona Project, bringing in inferior but thus far adequate water from he Colorado River. Unfortunately we still are facing burgeoning population in the face of limited & even shrinking water supplies. Arizona, traditionally dry, faces a long term forecast of being even drier, with no relief anytime soon.

Water can however be had, but at increasing costs. Imported water from the Colorodo River is becoming more expensive due to pumping costs, and is resulting in increased mineralization, as the percentage of it compared to local water increases. Whether to start treating this water to bring its mineral contant back to existing standrard is being debated. It can be done but at the cost of increased water rates.

Even this water will become insufficient in not too many years, and what to do then? Options include, in theory, the possibility of desalinizing and pumping from the Culf of Mexico, or maybe from the Pacific Coast -- both expensive propositions, the former with international complications. That leaves basically only one source remaining: reclaimed local effluent. This is already being used here, to some extent, for landscape irrigration; but treating it to potable standards will be costly. There are 2 things no one wants to hear about around here: poor quality water and expensive water; but the situation is forcing us into one or both.

There is one possibility that does not yet appear to have been discussed, and that is a dual water system. We have one already: in addition to the standard potable network, there exists a reclaimed-effluent network which reaches certain specified users such as golf courses and traffic medians to water their landscapes. Why could not this be expanded upon: expand the reclaimed effluent system to reach the entire city wherever the potable system now does, with outside faucets used for irrigation connected to the reclaimed effluent system, and the more sensitive used such as cooking to the potable system? Of course one could argue that with houses becoming very much tighter together in today's development schemes due to booming population and more land restrictions, there are few plants being planted outdoors any more, and those which are being installed tend to be arid-land species; and lawns are virtually nonexistant in new development, and are being ripped up even in old developments because watering them is becoming unaffordable -- so there won't be any private outdoor watering anyway, so what good would an expanded effluent system do? Well, there are still toilets to flush, which will continue to account for a substantial portion of water use. Is there any reason why toilets could not be flushed with reclaimed effluent?

Minimally reclaimed effluent requires minimal treatment and therefore can be furnished at less cost, which makes sense if the greater part of water useage can be satisfied using it.

And one other significant non-drinking use in a desert is in evaporative coolers. Could evaporative coolers be run with minimally treated effluent? Some serious health and odor questions would have to be answered; although evaporative coolers are becoming obsolete, as today's stringent building codes had made new construction extremely well insulated; and heat pumps have become more efficient.

Of course, a dual water system would not be without cost -- mainly for infrastructure. It means a whole second network of pipes, meters, etc. But those costs need to be compared against the costs of building treatment plants to be able to convert large quantities of effluent to drinkable and palatable standards. On the other hand,  some people even today are buying bottled water for their drinking (largely needlessly), at a much higher cost per gallon that city water; although admittedly they probably do not wash their clothes in it. And I suppose washing clothes in minimally treated effluent is not an option.

[MOD EDIT - PLEASE ENSURE THAT SUBJECT HEADINGS ARE PHRASED AS QUESTIONS, IN LINE WITH FORUM POLICY]

[another_someone]

I would imagine it is not just a matter of washing clothes, but washing themselves that would be an issue.  Water for drinking is generally only a very small fraction of the use of domestic water.

The other problem with excessively recycling water, in whatever manner, is that you would expect a buildup of impurities upon each cycle.

For instance, if you use impure water in evaporation systems, then I would imagine that you will leave residues that must be disposed of.

If you use impure water for irrigation, then you are feeding those impurities into the soil.  Some of the organic impurities may not be that bad, and may even help the fertility of the soil, but increased levels of salts could become a problem.

This is not to say that I would dismiss dual system water supplies, only that they can still bring their own long term problems that must be handled in some way.

I would also ask whether, in an environment where there is a shortage of water, using water for evaporative cooling is necessarily the best use of such a resource, and whether other cooling technologies could not do as well?

George

[Atomic-S (OP)]

quote:I would also ask whether, in an environment where there is a shortage of water, using water for evaporative cooling is necessarily the best use of such a resource, and whether other cooling technologies could not do as well?

Well, the problem with other technologies is that they use considerably more energy. That is why until recently, evaporative cooling was the method of choice for many users, particularly in older buildings in which refrigeration would be impractically expensive.

[Atomic-S (OP)]

quote:If you use impure water for irrigation, then you are feeding those impurities into the soil. Some of the organic impurities may not be that bad, and may even help the fertility of the soil, but increased levels of salts could become a problem

This is probably going to become an issue at some point, although has not occupied center stage in current debates. One issue is that Colorado River water, which the area is increasingly having to rely on, is harder than local groundwater, and the hardness is going to rise from about 350 ppm now to about 650 ppm eventually. That is becoming a matter of discussion, and the water utility is conducting taste tests to see if that is acceptable, or if they are going to have to treat it down to 450 ppm. If they have to, it will raise water rates, and also create a salt disposal issue, which presumabley can be managed in some manner. But if they do not treat, all those salts go into the main water supply and eventually appear in the environment regardless. Those salts, however, are mainly of calcium and magnesium, which are indigenous to our soil anyway, so that is likely not a huge problem. What may be more of a problem is if people, to combat 650 ppm in their laundry water, start installing water softeners, which will lower this at the expense of putting higher levels of sodium into the effluent. That could be more problematic.

[Atomic-S (OP)]

quote:For instance, if you use impure water in evaporation systems, then I would imagine that you will leave residues that must be disposed of.

That is true. Right now the most familiar example is the evaporative cooler, which, owing to existing water hardness, builds up large quantities of scale, which eventually causes a lot of trouble. There are ways of dealing with this, the best (from a machine standpoint) being the bleed-off line, which discharges a small but steady stream of the water from the system, which prevents the mineral content from exceeding some value. This substantially reduces the scale problem, but does not totally eliminate it. This discharged water is, of course, much harder than the source water, and must go someplace. Many people discharge it onto their plants, but this is not advised because the high mineral content is bad for many plants, but can be managed by moving the hose around and not putting too much of it on any one plant, relying upon straight water for the rest of the plant's water needs. You speak about the ultimate build up of salts if the municipality keeps recycling the same water, and of course that is true; water evaporates but salts don't, and they MAY tend to stay around; then again, they might be removed from the area by means similar to that of the evaporative cooler -- pump them out in a very hard solution to some remote site.

[Atomic-S (OP)]

Regarding the salt problem, there are certain things that have to be considered. One is that the municipality would never be relying SOLELY upon recycled water for its supply; there would always be at least some new water coming in. That water would contain salts, but at a limited level. Even so, of course, the salts that do enter will (very possibly altho perhaps not inevitably) remain here, or at least they will tend to, and eventually that would create a problem. Recycling this water at some point will require salt removal from at least part of the water, to make it acceptable for certain uses. So salt will be being taken out of the system eventually. Because such salt is removed at the treatment plant, it is very controllable, and can be further concentrated and then there are many options. The option currently mentioned is to sell it to a cement plant.

[Atomic-S (OP)]

If local raw water were to reach 700 ppm hardness, and they were to decide to treat half of it: the one half minimally for irrigation and toilet flushing, and the other half to 0 ppm for drinking and washing, then the net household discharge would be the average of those 2 numbers, which would be 350 ppm, which would be what current ground water is anyway, which therefore would add no new hardness to the ground water.

[Andrew K Fletcher]

A long long time ago, I postulated on using waste water to enrich the desert soils transforming them once again into fertile forests, but with a goal. That goal was to remove the thermal barrier from the baron often-concrete / tarmac coastlines by introducing trees close to the ocean. This damping down of the most important strip of soil on a continent would enable moisture to cross from the ocean onto the land and fall as rain. We have the Saudi, Kuwait, Israeli, Pakistani and Australian Governments interested, and Europe has a massive surplus of salt free waste water, sewage and farm waste. We have massive crude oil carriers transporting sea water half way around the world as ballast for no financial gain “Madness”. 

The domestic grey water use is vital also and should be in every home in Arizona.

So should Rainwater harvesting.

America can easily resolve the desertification process, they just need to change their mindset. Perhaps this latest recession will remind them of the dustbowl and focus their attention on the need for good soil and land management. Who knows?

Anyway, please view the videos on you tube and please leave a comment or 3.

Andrew