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What if mandatory rainwater harvesting isn't enough?

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When it comes to conserving potable water, no one says the city of Flagstaff and its residents aren't trying.

Studies show that the city has one of the lowest per-capita water use rates in Arizona -- and that even includes NAU students and all those summer tourists.

But as the city tries to wring even more conservation out of its residents, it has moved from voluntary incentives based on price to mandatory water schedules.

And now it might be about to mandate one type of nonpotable water source that will inevitably drive up the cost of construction -- and might not work.

The city's main water supply problem is tied to peak use. For 10 months out of the year, water use of about 8 million gallons a day is well below capacity of about 19 million gallons a day. But during May and June, when many residents turn on the sprinklers to water their lawns and gardens, the city's deep wells, Lake Mary and the Inner Basin pipeline are taxed to the limit. (The last, which delivered up to 3 million gallons a day, is off-line indefinitely due to landslides after the Schultz fire.)


The first city tactic to drive down peak use was to set water rates by tiers of use -- the more water used, the more expensive it got.

But the city found that many homeowners and businesses simply decided to pay the higher rates -- their water bills often doubled -- for two months in order to keep their landscaping lush.

Next, it implemented an every-other-day irrigation plan and banned all watering of any kind between 9 a.m. and 5 p.m.

Together, the two strategies, according to city studies, appear to have cut back potable water use during the peak months by about up to 15 percent.

To further relieve pressure on the potable water sources during the dry spring months, the city invested tens of millions of dollars in converting its two sewage treatment plants to Grade A recyclable effluent. That water is then sprayed on parks and ballfields as well as golf courses -- the latter are prohibited from using potable water. That has cut back potable water use by another 20 percent.


Now comes another step up the conservation ladder. Instead of just regulating peak use by price and watering cycles, a citizen panel has proposed requiring an active rainwater harvesting system -- tanks and cisterns -- for any new business and apartment or townhouse complex that doesn't plant native, drought-tolerant plants. The panel considered adding new, single-family housing, too, but pulled back -- for now.

The move stops short of what many conservationists would like the city to do: Ban the planting of non-native, drought-intolerant plants altogether. But even the top-down regulatory types on the Flagstaff City Council have been unwilling to go that far -- and besides, it might not pass legal muster.


So now, developers of office buildings and multifamily housing could be faced with a choice: Plant drought-tolerant landscaping and avoid some hefty extra costs -- a below-ground tank system for an office complex or strip mall can cost up to $100,000. Or go with nonnative plants and install either a rain-harvesting tank or a graywater system and hope there's enough supply to get them through the two driest months of the year.

A quick check of the weather records, however, shows just how problematic it is that a rainwater harvesting system will work for nonnative plants at large complexes. May and June in Flagstaff typically see less than 1 1/4 inches of rain combined, not enough to produce the tens of thousands of gallons a month that a typical landscaped commercial property requires. And even the month before isn't going to generate much excess rain to store -- average precipitation in April is just 1.3 inches.

As a result, developers are likely to have gone to the trouble and expense of installing an expensive rainwater harvesting system but have to supplement it with plenty of potable water, anyway.


There's another nonpotable alternative, and it sets up the potential for a new cottage industry in Flagstaff: Hauling inexpensive reclaimed wastewater by truck from the treatment plant to the office building or apartment complex in need of watering. Builders who do the arithmetic are likely to find it is cheaper to pay a hauler on an every-other-day schedule for two or three months than install extensive collection systems that might not get the job done anyway.

Of course the city could frustrate these budding entrepreneurs by raising the price of reclaimed wastewater to the point of unprofitability.

But for now, the council has farmed out the proposed rainwater harvesting mandate to several city commissions for further input. We hope those panels cut through the mixed signals the proposal is sending and get to the basics: What is the maximum amount of potable water that the city should be using during the driest months? Then, what are the most cost-effective and fairest ways to stay within that cap?


-- What if, for example, the city expanded the reclaimed wastewater pipeline system farther into commercial and apartment zones? How about residential neighborhoods? How would that investment compare, for example, to the hundreds of millions of dollars it is likely to cost to run a pipeline from Red Gap Ranch east of the city?

-- What if the city set prices for potable water that were not just three and four times higher than normal above a certain use level during May and June but 10 or 20 times? How many households with nonnative plants would switch to truck-delivered reclaimed wastewater? Would entire blocks and neighborhoods sign up for a delivery service?

If requiring rainwater harvesting for certain buildings with nonnative landscaping comes out on top, so be it. But we have a feeling there are other pricing and supply options to reach water conservation benchmarks that don't involve mandatory rainwater harvesting installations that drive up the cost of construction in an already expensive city.



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