23 Oct 2013

Low flush fallacies

VZ asks:
You say that low flush toilets are not that useful, but what about all the other usage of water in the household (shower, dishwasher, laundry...)? Does that water also get filtered in the same way (and hence it doesn't matter if you use less of it) or that's a different system and it makes sense to use less? Well, it makes sense to use less anyway (financially), since that's the ways incentives are setup, but just wondering about the environmental benefits.
First of all, it makes sense to use less water if you have a water meter and the cost of additional water ($) is not worth the benefit (happiness).

But, second, the entire concept of charging for water use needs to be put into the context of the water system, i.e., will water that goes down the toilet and drains be available, after treatment, in the environment (or as recycled water returned to customers for landscape irrigation or for drinking)? If that's true, then "efficiency" in terms of less water per shower, flush or wash will not really translate into any saved water.

Third, the real target for water savings should be outdoor use -- mostly landscaping  -- since that water tends to evaporate and/or sink into the ground, from where it cannot be reused.

That's why I think that outdoor watering should attract a higher charge (scarcity) or ban (shortage). Water budgets, by the same logic, do not make sense if they "lock in" a certain allowance of water for landscaping. That's why they are a bad idea in water-scarce areas and a waste of time in water-abundant areas.

Bottom Line: Flushed water does not disappear, worthless. It has value because it can be used again.


JBD said...

Speaking from an inland California perspective needless evaporative loss(consumptive use) shouild be the primary target as the water that sinks into the ground is generally not wasted or lost either.

Water allowed to percolate helps in three ways a) helps to counter overdraft, b) mitigates the concentrating effects of consumptive uses....the salts in the waters (naturally present) remain after most consumptive use...50% CU = 100% higher concentration, and c) it helps maintain the flux or flow of groundwater that keeps things moving and not accumulating.

Frankly groundwater recharge needs to be part of the environmental water budget (per your ABCDEF post).

Evaporative cooling is a consumptive indoor use that has the same detrimental effects.

The flux or flow of water is important in regards to indoor use too as it keeps the organic wastewater load (which is pretty constant with or without efficient water use) moving in the sewers and keeps the recycled water salinity low enough that salt removal (reverse osmosis) isn't required for general reuse.

Of course consumptive use provides much happiness......the trick is to have those who desire such happiness to pay the cost of their impacts, and not rely on others to absorb the costs.....ie developers who demand efficiencies from others to hand them cheap "surplus" water while sticking their benefactors with the cost of mitigation/treatment, rather than building the mitigation/treatment systems themselves to develop their own surplus/new water directly. (This is why much of the water saver handouts in schools are sponsered by building associations, or the like).

Of course we can choose to absorb the costs to be growth friendly, but that's not how water conservation is typically sold/mandated.

Personally I enjoy my long showers and don't get upset when I have to flush twice on my low flow toilets, but I have a small lawn and capture and percolate much of my rainwater in the winter to help counter my consumptive use effects during the summer.

When meters are installed (coming soon) I'll probably cut back a bit more on non-consumptive uses to save a few $$ on my monthly water bill, but I'll expect to see other long term costs rise...ie wastewater fees, or even food....to deal with the consequences.

Matthew Heberger said...

David, I'm surprised at your blanket generalization. Sometimes reducing withdrawals matters a great deal.

So I disagree with your premise that saving indoor water doesn't matter. In many of the largest American cities -- New York, Boston, San Francisco, Los Angeles -- water is intercepted high up in mountain watersheds and piped to coastal cities. Sewage is treated and discharged to the ocean, where it doesn't do any good. There is a real value to the ecosystem to reducing overall withdrawals. It means more water in rivers to support fish, wildlife, and recreation.

Your argument does hold water (ha!) for some cities astride big rivers. Cities like Saint Louis withdraw water from a river upstream of the city, filter it, distribute it, then discharge treated sewage downstream of their city, where it becomes part of the water supply to the next city downstream.

And in cases like San Antonio, where groundwater withdrawals are implicated in reducing springflows and reducing habitat of endangered species, there is a huge value to reducing withdrawals. Indoor conservation is a LOT cheaper than the engineering solution (piping hightly-treated sewage back to where it is injected into the aquifer.)

jqkeller said...

From a water perspective you may be right about low flow devices, but I think you should consider the impact on the sewage treatment plant. The treatment plant still has to treat all of the water which is an energy intensive process before the water can be recycled or discharged.

In most of the greater seattle area, the majority of the savings from fixture change outs comes from the sewer ccf charge savings, not the water ccf savings.

PM said...

You are missing the boat on water budgets and I'd like you to reconsider. I urge you to study a bit more about water budgets and how they are being used both within and outside of water rate structures to better manage irrigation demands.

Unless you believe there should simply be no outdoor water use in the American West (not a very realistic position), water budgets are an important tool for targeting inefficient customers and reducing wasteful outdoor use. Nothing about a water budget need be "locked in". That is false. The budget can be set based on the availability of water as well as the needs of the landscape and adjusted annually, monthly, whatever is necessary. A landscape water budget target is the only way that I am aware of to communicate if outdoor water use is reasonable and efficient to a large number of customers. Without a water budget there is no way to empirically determine if the water use at a particular property is reasonable or not. Set the water budget however you choose, but once a customized budget is developed for each customer, the utility has an extremely useful benchmark for comparing against actual use.

I agree that outdoor use should be the #1 focus of most water conservation programs, but by dismissing water budgets you are tossing out one of the most effective management tools available to a utility. In fact, water budgets can be useful even in water rich areas - even it water is abundant, there is no cause to waste it.

My 2 cents. I hope you'll open your mind a bit on this topic.

David Zetland said...

@All -- thanks for the excellent comments.

@PM -- I'd go for summer rates charged for consumption in excess of winter ("indoor") use as a basis for a budget, but I'm against putting lawns into the "cheap" block of a budget. You?

@jqk -- good point. I'm guessing that it's cheaper to recycle more water in scarce areas, but cheaper to reduce sewer flows where water's so abundant that it's cheaper to take more than recycle.

@Matthew -- I guess that SF et al. should move to toilet to tap, but their topography doesn't exactly mean that additional flows are costly (SF makes money on flows, right?), even from an environmental perspective where the water is left in the reservoir (rather than put in a river) if it's not used.

Your St Louis example fits my original post (thanks), but I guess that San Ant. is maybe the lead candidate for recycling to the tap. What do you think?

jbd said...

@jqk is right to an extent that energy to move water is important but the primary energy use at wastrewater treatment plants relate to processes based on organic/chemical load, which is a per person thing more than a flow thing...treatment plants in Europe are rated by population rather than flow as recognition of that. My concern is that water used too much can concentrate natural salts so much that the reverse osmosis trigger gets pulled to meet discharge requirements....sending the energy requyirement through the roof!

@Matthew has it right that logation on the watershed is everything....generally upstream locations should minimize reuse becasue the releases to the hydrosphere are then as high a quality as possible, since they WILL be reused....and those further down the shed near terminal drainage (ie the coast) should maximize recycling as that minimizes upstream effects from their imports (ie Hetch Hetchy), plus their portion of the hydrosphere can handle the added salinity in discharges w/o affecting downstram users, or if they choose to use reverse osmiosis they have somewhere to discharge brine at much less cost than upstream folk....in fact the brine would help make their fresh wastewater discharges to the ocean less toxic for that environment.

Matthew Heberger said...

Dave, water recycling is great, but it’s better not to use water in the first place. There are lots of benefits to reducing withdrawals and leaving water in the environment!

In the case of San Francisco, water that is left in the Hetch Hetchy reservoir means more stored water carried over to the next year, increasing water supply reliability. And it could also mean more water is available for instream flow. This is a BIG benefit to the fish or the boaters on the Tuolomne River, or for water quality in this little downstream area we call "the Delta." :)

David Zetland said...

@Matthew -- My point is that there's a sweet spot for every system, and that reductions in demand are neither 100% good from an economic perspective, given the impacts on financial stability for utilities that cover most of their costs from water sales or for those -- like SF -- that NEED minimal wastewater flows to keep sewers clean (remember that they needed to use bleach to clean lines a few years ago)? So, I'd like to agree with you, except for the institutional details that bring costs with the benefits from reductions in demand. And we haven't even got to the cost/benefit of conservation measures vs value of water to consumers! Agreed?

Anonymous said...

I have read that in some older parts of Tucson, Arizona, installation of low flow devices resulted in insufficient water to carry the waste (because the slope of the pipes was not steep enough).

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