Desalination vs. A National Water Grid

by Brian Dunning
June 22, 2021

The Earth is warming due to human-caused climate change, and we are already deep into the severe weather systems that causes. Even if all carbon emissions were stopped today — an obviously ridiculous scenario — we'd still be looking at a minimum of a century of increasingly drastic weather. The Earth is warming for sure, but it's not drying up; warmer temperatures cause increased evaporation, more water in the atmosphere, and thus more powerful storms. So while places like the American southwest are drying up and are in extreme drought every year, other parts like the southeast can expect heavier rainstorms and higher annual precipitation. Like all of Earth's landmasses, the whole North American continent is too complex with too many systems with too many variables to provide an easy answer like "Will we have more or less rain overall in the coming century", but what the climate models do all agree on is that weather events of all types will become more frequent, more severe, and less predictable.

So that's where we are. Places now in drought will see worse. Places with flooding now will see worse. If nothing's done, well, then we might as well end this episode right here. But that's not the goal. Today we're going to see what can be done about it, and we're going to pit two potential solutions head to head: desalination vs. a national water grid.

Apologies to many listeners, but by definition this episode is going to be very US-centric. It's impossible to talk about all the world's complexities at this level of detail in a 15-minute show. But the concepts discussed today do certainly apply to everywhere else on the planet.

Desalination

There is one thing that can be done to at least help with one half of the problem: desalination, which can create fresh water from seawater or brackish water, and pump it to inland reservoirs. At a glance, desalination appears to be the panacea: our oceans provide a source of water far greater than we could ever need; all we need is the right equipment running affordably to keep all of our reservoirs brim-full to feed our agricultural, industrial, and domestic needs. And that wastewater then flows right back into that very same ocean. It's the perfect win-win.

But then come the problems. There are three basic problems. But before discussing them, we should talk about the history of desalination.

It is the history of the development of the Middle East. As the Middle East oil states grew, they needed water to feed their explosively growing cities. The Persian Gulf was the only option, and so it became as it is now: lined with desalination plants. Back in the day, the technology was thermal separation; basically just boiling the seawater to get nice freshwater in the form of steam, and a bunch of leftover hot brine which was discharged back into the Gulf. Thermal separation was inefficient, costly, and produced the saltiest waste. Most of the Persian Gulf's desalination is done on this old equipment which, given their wealth in fossil fuels, is not likely to change.

Fast forward a number of decades into the modern era and we find the newer technology, reverse osmosis, which is basically just filtering out the salt. It's much more energy efficient and produces much less salty waste, and it's what most of the rest of the world has used ever since. With the exception of a few other technologies and some experimental ones, reverse osmosis is what would be used in most any new plant today. Moreover, it's improving all the time, as new filter membranes continue to be invented to both reduce costs and reduce the energy needed to push water through the membrane at lower pressures.

So now, the three problems. First is that cost. The plants are expensive to build, but mostly, they're expensive to operate because they use so much electricity. Even the reverse osmosis plants, which are the cheapest, still suck up a lot of power. Second is the source of that power, which for most stations, is still fossil fuels. Releasing more carbon to try to keep up with a problem caused by releasing carbon is hardly a good strategy. Thus, it's crucial that future desalination plants be fueled by renewable, carbon neutral sources.

Third is the problem you've been waiting for, and that receives an outrageously disproportionate amount of attention: all that brine. Just as a sample, listen to these headlines to gauge the public mindshare absorbed with the brine waste problem. From WIRED:

Desalination Is Booming. But What About All That Toxic Brine?

From BBC News:

Concerns over increase in toxic brine from desalination plants

And even from Scientific American, which some years ago began its own Nat Geo-style transformation from respected science publication to clickbait machine:

Slaking the World's Thirst with Seawater Dumps Toxic Brine in Oceans

There's really only one type of publication where you won't find these headlines: the science literature. Oh, the studies of brine and its effects are out there, to be sure, so you will find them: but you'll find them soberly discussing the issue in context, and not trumpeting doom and gloom.

First of all, nearly all of these articles discuss the effects in the Persian Gulf, dumping ground for fully half the world's brine waste. The Persian Gulf relies largely on the old thermal system, and these plants often do not have or follow environmental regulations. But most of all, the Persian Gulf is where these studies are done because — even before desalination began — it was already the world's saltiest arm of the oceans. That's because it's essentially a salt sink; it loses most of its freshwater to evaporation, and has only one small inlet where the current is always flowing inward to replace that evaporative loss: the Strait of Hormuz.

But as for the rest of the world, with over 16,000 desalination plants operating in over 175 countries, the industry is evolving very quickly as new ways to reduce costs, improve efficiency, and meet ever-stricter environmental regulations are being developed. This includes profitable recovery of the many minerals and other valuable elements found in brine — which reduces the impact of returning it to the sea. So it's hard to characterize the real brine issue; anything said today is out of date by tomorrow.

Waste brine from a reverse osmosis plant averages somewhere around just over 5% salt compared to around 3.5% salt for pure ocean water — not nearly as different as some doomsayers claim. In many cases it's then diluted with enough seawater to bring its concentration down to almost match. It's then piped out to sea (in the United States, at least seven miles and 500m deep), always to a location identified by a hydrographer optimal for dispersion and catching currents, and sprayed into the currents with widely spaced nozzles all intended for maximum dispersal and minimal collection on the seafloor. This is the best case scenario for nearly all modern plants being designed and built today, and it's a far cry from what the Persian Gulf did in the 1960s. Not in all cases, but in many, the environmental impact of a modern reverse osmosis plant truly can be negligible. In any case, sea life vacating a particular patch of ocean floor hardly compares to the environmental catastrophe ashore if nothing is done to avert unprecedented drought.

So now let's look at an alternative to making new water: moving the water we already have and that we're going to soon have even more of, using a national water grid.

National Water Grid

In the simplest terms, a water grid is a system of high-capacity pipelines that interconnect all the nation's largest and most important reservoirs. Any region experiencing a water surplus can avoid flooding by sending its excess water to regions experiencing a shortage. Ideally such a system, properly configured and managed, can virtually eliminate both catastrophic floods and catastrophic droughts, all while keeping crucial aquifers topped off and healthy, and restoring ecosystems throughout all the affected areas. Some countries, notably Australia and India, are actively planning or already constructing national water grids.

The simplest possible iteration of a water grid in North America would be a pipeline taking water from the Mississippi River to the Colorado River. The major reservoirs on the Colorado, Lake Powell and Lake Mead, could thus be kept full year round, and estimates are that the entire construction cost would be cheaper than the disaster recovery costs of a single major flood in the Mississippi basin. The project literally pays for itself in the first year, and that's to say nothing of the economic benefits of all the agriculture of the southwest suddenly having all the water it wants, forever. Even an expanded grid bringing water from areas of increasing flooding and distributing it to reservoirs farther north and west of the Colorado would make and save far more than it would ever cost.

The problems with this are mainly legal, but also environmental. The legal issues include historically thorny problems like water rights and interstate politics, which might make the science-minded bristle but are sadly the reality we live in. The environmental impacts are overwhelmingly positive ones, except for two that present interesting head scratchers.

First of these is non-native species. Moving water from the Mississippi to the Colorado means harmful species like the Quagga mussel, cryptosporidium, Giardia lamblia, E. coli, and total coliform bacteria would have to be mitigated along the way, according to the law. However these species all already exist in the Colorado; Quagga mussels were first found in Lake Mead in 2007 and are already a problem for the hydroelectric dam machinery. So this is a question to ponder. On the one hand, we have good reasons for invasive species mitigation; on the other hand, the cat's already out of the bag and we have to do something to save the country from the next century of worsening drought and flooding.

The other problem is the environmental impact of dams. Currently we're in an age where we want to remove old dams and restore fisheries and native canyon ecosystems. But a water grid (and to a lesser extent desalination) would depend heavily on a robust, widespread network of dams and reservoirs. The two simply don't go together. We can continue removing dams in smaller canyons that are not crucial to a water grid, but both interests focus their attention on the biggest, most popular canyons where we have the most important reservoirs and also the most impact from dams. Again, there is no easy solution to this one, and none that many will find satisfactory. As global warming continues to worsen our water problems, these questions are all likely to be resolved, in the end, toward solving that.

And the winner is...

Maybe we shouldn't have caused global warming in the first place; but there's little to be gained now by crying over that. Obviously, stopping all use of fossil fuels now is an imperative in every way, or else a century from now we'll be wondering how do we amplify these solutions by a factor of ten or a hundred. If the point of today's episode was to find a winner between desalination in the west and a national water grid everywhere, well, there can't be one. We can't afford to not go all-in on both. Both present challenges both environmental and bureaucratic, but the answer is clear. Vote. Vote desalination, and vote water grid. We'll save lives, save the economy, and perhaps do more good than any other possible human project could.

By Brian Dunning
Follow @BrianDunning