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Desalination or Reuse? Here’s How Much New Water Supplies Will Cost

A new report from the Pacific Institute looks at the comparative costs of different water efficiency and supply options that could help supplement California’s water, including desalination, water reuse and stormwater capture.

Written by Tara Lohan Published on Read time Approx. 4 minutes
The Carlsbad, Calif. desalination plant, seen in a Friday, Sept. 4, 2015 photo, borders Interstate 5 on one side and the Pacific Ocean on the other in Carlsbad, Calif.Lenny Ignelzi, AP

Anyone who’s followed California’s unfolding water problems, compounded by the most recent drought, knows that there are supply problems reflected in declining groundwater levels, struggling ecosystems and bitter battles among stakeholders over resources.

It’s also clear, when it comes to solutions, there is no silver bullet.

“That means we are going to have to do a lot of things, but the need to do many things doesn’t mean that we should or could do them all at once,” said Heather Cooley, water program director of the Pacific Institute, a global water think tank based in Oakland, California.

Cooley and Pacific Institute colleague Rapichan Phurisamban coauthored a report released this week that provides an economic framework to begin comparing supply and demand solutions in California to help determine what the best options are for increasing California’s water supply.

“We are still growing as a state, we are still faced with climate change, we still have a need to restore our ecosystems – we need to be looking at what the alternatives are to meet our future needs, and the good news is that we have lots of options,” said Cooley.

The report considered demand-side solutions focused on cutting water use via conservation and efficiency. It also looked at ways to supplement supply including stormwater capture, desalination of seawater and brackish water, nonpotable reuse (water used for nondrinking purposes such as irrigation) and indirect potable reuse (recycled drinking water that is first stored in an aquifer).

In this May 6, 2016 file photo, a pipe feeds recycled wastewater to a holding pond to recharge an underground aquifer at the Orange County Water District recharge facility in Anaheim, Calif. (Chris Carlson, AP)

In this May 6, 2016 file photo, a pipe feeds recycled wastewater to a holding pond to recharge an underground aquifer at the Orange County Water District recharge facility in Anaheim, Calif. (Chris Carlson, AP)

Their research concluded that conservation and efficiency are the cheapest ways to boost supply, but there are also a number of other strategies that vary by region.

When it comes to conservation and efficiency, California has already made substantial progress since the 1980s. In many areas, per capita water use has fallen or remained steady despite population and economic growth. But, Cooley said, there is still ample room for more gains to be made by both residents and businesses.

The biggest savings at the residential level come from landscapes, followed by fixing leaks, and then installing more efficient toilets, clothes washers, shower fixtures, faucets and finally dishwashers. Just installing low-water use landscapes could net 870,000 to 2 million acre-feet (107 million to 2.47bn cubic meters) of water a year. And most conservation and efficiency improvements are cost negative, meaning they save a homeowner or business money in the long run.

In order to get more people to embrace these changes, public education may be needed but also proper incentives. Low costs for water or rate structures that don’t communicate the value of water means that homeowners don’t have an incentive to convert, said Cooley.

“Many utilities provide rebates, but we could also be doing a lot more of that,” she said. “I think our results demonstrate a strong economic case for more quickly investing in those measures as a way of meeting our water needs,” said Cooley.

For supply-side projects, the report found that the cheapest options are large projects that capture stormwater. The median cost per acre-foot of water for large stormwater projects was $590. Seawater desalination was the most expensive, with median costs ranging from $2,100 an acre-foot for large projects and $2,800 an acre-foot for smaller projects, with some smaller projects reaching over $4,000 an acre-foot.

The second least expensive option after stormwater capture was brackish desalination (much cheaper that seawater desalination because it requires less energy and treatment). Next was nonpotable reuse and then near in price but just a little more expensive was indirect potable reuse. But the report notes that the cost of building new distribution systems of purple pipes for nonpotable reuse can bring the cost up and may not be as cost effective in some cases as indirect potable reuse.

The study did not examine direct potable reuse, where recycled water is piped directly to customers after treatment through the existing distribution network and not first stored in an underground aquifer, because the state does not yet have regulations for it, although they likely will in coming years. “Once the regulations are in place you will see more communities considering it,” said Cooley, but “the need for it will depend on different factors.”

As with all supply-side projects, regional considerations are key. For example, indirect potable reuse and stormwater capture require a groundwater basin in which to store water, which not every area has. When it comes to inland areas, water recycling could be tough if there are downstream users that depend on those outflows of wastewater. And of course if desalination makes economic sense anywhere, it would be limited to coastal communities.

But analysis of which options work best for which region is precisely the kind of work that local water managers should be doing, said Cooley.

“We hear a lot about the challenges we face, but there are a lot of opportunities out there,” she said. “We just need to have the information and the conversations about how to most effectively invest in those.”

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