Water: Supply and Scarcity
Is the glass half empty or half full?
Key Takeaways
- Many regions in the US face water “stress” — the margin between water supply and demand is slim in times of drought. Stress happens when freshwater reserves — both surface water (reservoirs, lakes, rivers) and groundwater are being used faster than they are naturally replenished.
- Factors contributing to water stress: changes in seasonal weather patterns, shifts in population density to drier climates and cities with outdated infrastructure, increasing agriculture demands. While the average amount of water used by the US has gone down since 1980, areas in California, Florida, Texas and Arizona are increasingly susceptible to water scarcity.
- In the US, thermal power plants (coal, natural gas, nuclear) are still the biggest consumers of water (42%), although the amount of water they use has fallen since 2005. Roughly 37% of the water used in the US is for agricultural irrigation.
- Traditional solutions to water scarcity — building dams and surface reservoirs — are giving way to aquifer replenishment (using groundwater as storage) and desalination plants. There is continued buzz around Atmospheric Water Generator (AWG) technologies that capture water from air, though it’s still unclear what the cost of these technologies might be at scale.
In a recent post, I shared that concrete is the second most consumed material on the planet — after WATER. It’s pretty astounding to think about how easy it is in the US to find clean, drinkable water flowing out of a tap for free.
For those who live in the Western US, cycles of drought and a worsening fire season have become normal. Within the past five years, you may have also seen dire warnings about water shortages in other highly populated cities: Cape Town, South Africa; Sao Paulo, Brazil; and Cairo, Egypt as a few examples. Each region is unique, complex and faces different challenges.
In this post, we’ll dip our toes into where our water comes from in the US, the causes of water scarcity, and some technologies on the horizon that may help.
[Not] Wet Hot American Summer: Water Use in the US
The amount of water that the US supplies and uses is incredible — 322 billion gallons per day. For context, this equivalent to 84% of the Mississippi river’s flow, or roughly three Lake Tahoes-full of water per year. Of this, 74% is taken from surface sources: rivers, lakes, and reservoirs. The remaining 26% comes from groundwater pulled from the 60+ large underground aquifer systems that span the continent.
Despite what you may have heard about almonds, power plants are actually the biggest consumers of water in the US, representing 42% of freshwater withdrawals. This is water lost via evaporation from cooling towers [1]. Agricultural irrigation is the next biggest sink, accounting for 37% of water use. Of the rest, 12% of the water consumed in the US is provided by water utilities to residential and commercial customers like you and me. [2]
It would be easy to blame water scarcity on population growth, but that isn’t quite the full story. Surprisingly, total US water consumption has gone down since 1980, even while our population grew by 100 million people. [3]
So if the amount of water the US is using is going down, shouldn’t there be more water in reservoirs? Why are areas like California experiencing increasingly severe droughts and investing in desalination plants? Why does the Colorado River no longer get to Mexico?
Many factors have contributed, and the answer is highly location-dependent. Although the total amount of rainfall the US gets each year has stayed relatively constant over the past 100 years [4], seasonal patterns have changed dramatically. Specifically summer precipitation levels have changed in Oregon and Washington have both trended significantly drier over the past 50 years.
California struggles with a trifecta of changing seasonal weather patterns that reduce snowpack, high agricultural demand in the Central Valley, and growing population demands in the southern part of the state. As temperatures rise, more water evaporates from rivers, lakes, etc. before entering the groundwater system, which also reduces the amount of water that is available.
In Florida, the large Floridan aquifer is strained by high water demand including from power plants. Several of the states with the biggest population inflows — Texas, Florida, and Arizona — are among those with slim margins between water supply and demand. A map based on comprehensive analysis from the World Resources Institute shows water “stress”, or how close an area comes to draining its water supply each year. In considering markets for technologies on the supply side of the water equation, or in evaluating locations for water-intensive businesses, this is something to consider.
A global problem. The US is lucky from a water scarcity standpoint compared to other parts of the world. In addition to water scarcity caused by environmental conditions and increasing population, increased pollution contributes to water scarcity in many countries. The World Resources Institute’s Aqueduct Project is a great tool to explore relative water risk around the world. For detailed future projections of water scarcity, I recommend this paper in Nature. The majority of the companies addressing water supply challenges that we meet are focused on markets outside of North America. Which leads us to…
Aqueous Solutions
Couldn’t resist the chemistry pun here. How are government planning agencies, municipal utilities, industrial providers and startups working to secure the supply of water?
Expanding surface reservoirs and building dams are classic strategies to store more water for long dry seasons and to protect against drought. For older dams, repairing and updating infrastructure, and removing built-up sediment from existing reservoirs can also increase water storage capacity. Building new dams and retention ponds can have serious ecological consequences, and reports on whether this solution will continue to be effective are mixed (one recent case study). See the EPA’s list of additional strategies here.
Aquifer restoration projects are increasingly common in the southeast, southwest and western states. These projects replenish groundwater by adding water back to the ground through injection wells, surface spreading or injection pits. The quality of water that can be injected depends on state regulations and how close the injection site is to a drinking water source. [5] Most of these projects aim to replenish water reserves that can be used in drought.
Desalination processes convert seawater or brackish water into fresh drinking water. Since about 40 percent of the world’s population lives within 60 miles (100 km) of an ocean or sea, this is a logical solution for water scarce cities near a coast. As a quick snapshot of desalination today: currently about 16,000 desalination plants are operating around the world, producing about 26 billion gallons of water per day (supplying less than 1% of the world’s water). In the US, water produced by desalination typically costs 2x or more than surface or groundwater sources. The cost of producing water through desalination is typically lower in the Middle East: $1.90 to $2.65 per 1000 gallons, versus roughly $6 per 1000 gallons in North America. Key challenges are the large amount of energy desalination plants need, and what to do with the super-salty water (brines) created by the process.
Two types of desalination technologies are common today: reverse osmosis (membrane-based) processes, and thermal desalination. Seawater reverse osmosis (SWRO) dominates capacity outside of the Middle East — this technology pushes salty water through a membrane (think of a thin sheet of plastic that acts like a filter, keeping salt out) to produce a freshwater stream on the other side. The amount of energy needed depends on the temperature of the water and how salty it is. [6] Improvements in membrane technology in the past decades have helped drive down costs and enable more adoption.
Thermal desalination uses heat to evaporate water, leaving the salt behind. The evaporated water is converted back to a liquid in a separate area to produce pure water. These processes are more common in the Middle East, where fuel prices are low and there is widespread use of facilities that co-generate power and water. Thermal desalination plants use more energy (higher OPEX) but have lower capital costs relative to reverse osmosis plants, though membrane costs are still coming down.
Atmospheric Water Generation (AWG), or capturing water (humidity) in the air is a newer concept with a lot of appeal. This technology would solve the problem of brines, and could be used everywhere — not just on the coasts. Even the Mojave Desert in the summer has about 10% relative humidity, which is 3 grams of water per kg of air at 90 degF. High costs are the main challenge for adoption, limiting the technology to military use, refugee camps, and off-grid or remote areas thus far.
While many types of AWG technologies are feasible and available today, it is difficult to do cheaply. Extracting this water from air is expensive and still takes significant energy, both to move enough air through the system, and to capture and re-release the water. [7] There are multiple approaches for capturing the water, most commonly condensing water directly on cool surfaces — think about sweat on a beer can, but bigger scale! New systems in development use sponge-like solid or even liquid materials.
Agricultural water efficiency can have a large impact on overall water use as some of the most water intensive sectors: 70% of global water use is for agriculture. Exploring this huge potential set of solutions, drip irrigation, better soil management, drought resistant crops, and one of our favorites, vertical farming (shout-out to Upward Farms!) will have to wait for now.
Household water Efficiency Technologies are the best bang for the buck, hands down. We should all install low-flush toilets and efficient shower heads, chose front-loading washing machines, and follow the DOE’s other suggestions for home water efficiency. (Full disclosure: I have done none of these. But they would probably save me money, make EBMUD happy [8], and would certainly be cheaper than the incremental cost of building another desalination plant.)
This is just the first part of the story. Stay tuned for future posts on water treatment and reuse, ocean technologies, and comparing investment opportunities in these sectors!
Notes
- Power plants that generate electricity from heat (coal, natural gas, and nuclear power plants) do this by boiling water to make steam, which turns a turbine. The steam has to be cooled back into a liquid to restart the cycle — a separate stream of cooling water is used to cool and condense the steam. This process heats up the cooling water, which is then sprayed into a cooling tower. The water droplets that evaporate in the cooling tower are is the water “consumed” by the power plant.
- The average American uses 80–100 gallons of water per day. If you’re curious, here’s a breakdown of how a typical US household uses water. Here are many more pretty graphs of water use by country, sector, and even the water footprint of different foods.
- Most of the drop in water consumption is due to less water use by thermal power plants. Many plants have retired (coal plants are especially thirsty), and the remaining thermal power generation fleet becoming more efficient. Here is a breakdown of US water use by sector since 1950.
- NOAA data shown in a blog by Christopher Burt shows a slight increase in average precipitation: from about 29 inches a year in 1901, to just over 31 inches a year in 2020 (with a LOT of variation year to year!). The biggest increases in annual rainfall have been in the Northeast, Ohio Valley, and Upper Midwest.
- Examples of Aquifer restoration projects in Southwest Florida (project cost: $33mm), Orange County, CA (project cost: $135mm)
- Brackish water has a salt content of <10,000 mg/L. The salt content of seawater ranges from 18,000 to 36,000 mg/L in the US, and up to 45,000 mg/L or more in parts of the Middle East. (For comparison, the amount of sugar in a Coke is about 110,000 mg/L.)
- In the Mojave desert example, the water capturing system would have to suck 1,260 kg (over a ton) of air through it to capture one gallon of water. This is assuming it captures 100% of the water in the air, leaving it bone dry — a high bar! Atmospheric Water Generation technologies are significantly more cost effective in humid environments.
- By the way, East Bay Municipal Water District (EBMUD) is still running Virtual Tours! Wastewater plants are super cool.
Prime Movers Lab invests in breakthrough scientific startups founded by Prime Movers, the inventors who transform billions of lives. We invest in companies reinventing energy, transportation, infrastructure, manufacturing, human augmentation, and agriculture.
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