Desalinated Water Doesn’t Have to Come From the Ocean

The California Department of Water Resources has awarded $34 million in grants to eight desalination projects throughout the state. The money is part of a round of awards for desalination projects, as designated by Proposition 1.

While ocean desalination has often caught most of the public attention, two of those construction projects, in Antioch and Camarillo, focused specifically on inland brackish desalination, as did several of the other projects that received grant money. California has plenty of salty inland water, such as the water in the upstream Delta or in underground aquifers that have absorbed soil salts. As local agencies look for more potable water sources, desalinating that local water may become an important part of the equation, says Richard Mills, the Department of Water Resources’ recycling and desalination chief.

But it’s not cheap. Mills says that brackish desalination can run from about $800 for an acre-foot of water to about $3,000. While these projects are generally cheaper than ocean desalination, costs vary significantly by location. Still, the proposed projects show that, despite the cost, there is still a lot of interest in brackish desalination. “That may mean that we’re running out of cheap water sources,” he said.

Water Deeply spoke with Mills about the projects and the role of brackish desalination, especially groundwater desalination, throughout California.

Water Deeply: In these awards, why is there so much emphasis on brackish desalination, as opposed to ocean water desalination?

Richard Mills: I think that cost and the sustainability of implementation accounts for a lot of that. The cost of brackish water desalination is generally much less than seawater desalination, in part because the treatment itself – the cost is very much affected by the degree of salinity. The less salinity, the less cost. The environmental issues can [also] tend to be somewhat less, depending on the individual situation.

Water Deeply: What are the current environmental impacts of brackish desalination?

Mills: For open water intakes for brackish water – from San Francisco Bay or the upstream Delta – you have the effects on aquatic organisms in the water column. Brackish water [desalination] growth in California has been more focused on using groundwater, where the intake part isn’t so much of an environmental impact, other than the effect on the groundwater itself and potentially overdrafting.

Brine is the other key environmental issue.

Water Deeply: Why is brackish groundwater desalination cheaper than seawater desalination?

Mills: I should say that, for either ocean water or brackish water projects, there is a very wide range of project costs. If you just look at the treatment itself, the desalination treatment technology is to take the salts out of the water, and the most common treatment technology that is being used currently is reverse osmosis, which can be fairly energy-intensive and the amount of energy required is greatly affected by the concentration of the salts in the source water.

For the brackish water projects, we seem to be dealing in the range of 1,000–3,000 milligrams per liter of total dissolved solids, whereas when we’re talking about ocean water, we’re more in the range of 30,000–35,000 milligrams of total dissolved solids. So you’re dealing with a concentration of salts that is about one-tenth that of ocean water, and therefore the cost itself is much less.

The brine is another significant cost, as well as an environmental issue. With ocean desalination, the quantities of brine are much greater, but one advantage is that you generally have the ability to discharge them into the ocean in an environmentally acceptable way. With inland projects, there’s the issue of what to do with the salts. Putting them in a landfill – could there potentially be contamination issues as salts leech back into the groundwater?

So we can’t say that in an individual situation, brackish groundwater desalination is going to be a cheaper alternative, but as you see from the eight awards there is still a lot of interest in it.

Water Deeply: How much do you think that brackish desalination will be a part of how California deals with water issues in the future?

Mills: In the California Water Plan 2013, we had kind of an inventory of projects that were in place at the time, and also what seemed to be in planning. In 2013, there were 23 brackish groundwater desalination plants, and three ocean desalination plants. The ocean plants, at that time, were very minuscule in size, so the annual production and capacity was only 560 acre-feet a year, whereas with the brackish groundwater, the annual capacity was 139,000 acre-feet a year.

Water Deeply: As brackish desalination becomes a bigger part of California communities meeting their water needs, how is the Department of Water Resources balancing brackish groundwater withdrawal with the Sustainable Groundwater Management Act?

Mills: Well, one thing is that when we give grants toward the planning or even for construction, we’re expecting that there be an analysis of how the drawing of additional brackish water from the ground may impact the overall groundwater supply.

With the Groundwater Management Act, there’s a mandate to analyze these issues. I think that even if there wasn’t a prudent local effort to analyze the impacts on the part of the proponents of local brackish groundwater use, the groundwater management agencies that are trying to comply with the Groundwater Management Act are going to be a driving force to make sure that proper analysis is being done.

Water Deeply: Thank you for talking with us. Is there anything else that you would like to say?

Mills: I think in summary, it’s not going to be on a statewide level a huge contribution to our state’s water supply, but it is important for many local communities who need a more significant source of supply, and it is a way to take advantage of a source of water that is currently unusable and being able to use it.

This article originally appeared on Water Deeply, and you can find it here. For important news about the California drought, you can sign up to the Water Deeply email list.