Western Water’s Paradox of Thrift

When I install a low-flow toilet, I use less water each time I flush. In the arid West, this is a good thing, right? Maybe. Maybe not.

In Albuquerque, essentially every gallon I flush, after treatment at our sewage plant, ends up in the river, available for downstream users. It’s called “return flow credit”, and serves not only as a debit on the water accounting side wherever the water is withdrawn, but also as a credit in the river.

Such is the counterintuitive being faced in Las Vegas now as “graywater” systems are being discussed, and being opposed by the very people you might think would want to encourage such efficiencies. From the Las Vegas Sun:

The Southern Nevada Water Authority wants that system preserved because it allows Las Vegas to consume more than its annual 300,000-acre-foot allotment from the Colorado River. Water returned to the lake converts to credits that the Water Authority can use to pump more water from the lake.

But some homeowners, builders and environmentalists watching this continuous loop wonder: Why not shorten the distance water travels by allowing homes to keep and recycle the water they use — what’s known as graywater? Water from sinks, showers and washing machines could be reused to more efficiently and cheaply water lawns or other landscaping, they say….

The water authority, after studying the idea, decided this year to make it official policy to oppose it.


  1. I am guessing that SNWA is also worried that customers are cutting them out of the loop — reducing water consumption that SNCWA can charge for — and thus revenue.

  2. Sure keeping grey water close to the source is a wonderful idea…in theory and for the future.
    Provided you start installing plumbing in new houses to take advantage of grey water it works for the future. But what about the millions of houses which currently exist, mostly with their plumbing entombed in slab.
    As far as I know there is no practical way to retrofit your typical house such that grey and black water are kept separate.
    if anyone knows of a way… by all means let me know I will be the first to implement this

  3. @jf
    I am trying to get maps of water use data to show these effects.

    @jf and DZ
    It seems that the short term win for water departments is in conflict with the longer term win for the departments and the longer term win for the town. It is, once again, the ‘multiperson prisoner’s dilemma’ where the best behavior for one prisoner is to the longer term detriment of all prisoners. Rewriting the incentives for water departments might change things.

    ‘This Old House’ seems to have had grey/black water retrofit suggestions.

  4. Another problem with widespread adoption of grey water reuse that is not widely discussed is that sewer systems are designed assuming a certain flow of fluids to flush out the solids. When that flow of fluids decreases, the system is not adequately flushed of the solids. I don’t know that the effect of this has actually been measured anywhere, but it has been cited as a concern by wastewater people here in Tucson, where greater use of grey water has been encouraged.

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