Elon Musk has said several times recently that desalinisation is “absurdly cheap”.1 

This was surprising to me. When I was younger I was taught the mantra that desalinisation “uses lots of energy and is really expensive”. And to be honest, I hadn’t thought about it much since then.

Cheap desalinisation would be very welcome indeed; not just to make societies more resilient to periods of water scarcity, but to relieve pressure on groundwater resources, and provide clean water to those that are already lacking.

I thought it was time to update my perspective and see what the numbers had to say about the prospects for desalinisation.

A few caveats to start:

• I’ll focus on energy use and costs here. I’m not analyzing the amount of brine water that’s generated and how to manage that in an environmentally-sustainable way. Not because that’s not important, but because this post would ‘“absurdly” long.
• To get a sense of the numbers, I’ll make pretty unrealistic tests like “every household in the US needs to get its domestic water from desalinisation”. Or “everyone in the world needs desalinated drinking water”. These scenarios are extremely unlikely; they’re just useful “what ifs” to understand scale.

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Desalinisation technologies

 

There are two key types of desalinisation technology: thermal desalinisation, and reverse osmosis.

Thermal desalinisation uses heat to evaporate the water (separating it from the salts and impurities) before condensing it back into a liquid. The salty brine water is left behind.

In reverse osmosis, pressure is applied to push water through a semi-permeable membrane, which removes the salt and impurities to leave freshwater on the other side. The figure below shows the “natural” process of osmosis where fresh and saltwater would want to mix to make the concentration of salts equal on both sides of the membrane.

In reverse osmosis (shown on the right), pressure is applied to overcome and reverse this.

 

Both technologies work, but thermal desalinisation is much more energy-intensive (and therefore expensive). It uses around three to five times as much energy per cubic metre of water.2

Most desalinisation plants today use reverse osmosis, and this is the process I’ll focus on in this article.

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Desalinisation has been getting more energy-efficient

 

Reverse osmosis technologies have become much more energy-efficient over the last few decades. You can see this in the chart below (although it ends in 2008).

In the 1970s, it would take around 20 kilowatt-hours (kWh) to desalinate one cubic metre of water.

Today that figure is around 2.5 to 3.5 kWh. It’s often suggested that the theoretical minimum for reverse osmosis is around 1 kWh. Think of this as the floor and the absolute best that can be achieved. No one is there yet, and seems unlikely that we’d get the process as efficient as this.

If we wanted to get energy use lower than 1 kWh per m³ we’d need to innovate and develop a different process.

For all of the calculations that follow, I’m going to assume that reverse osmosis uses 3.5 kWh per m³. I’m being quite (deliberately) harsh here because some desalinisation plants use less than this.

 

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How much energy would households need to get all of their water from desalinisation?

 

What would happen to electricity demand if countries were to get all of their domestic water from desalinisation?

The average American household uses around 1135 litres of water per day. Getting all of this water from desalinisation would increase its domestic electricity demand by around 13%.3

The average UK household uses less water: 349 litres of water per day. But it also uses less electricity, so desalinisation would increase its electricity demand by a similar share: 15%.

Let’s put this electricity demand into context for the United States. To do this, I’ll use data from the Energy Information Administration (EIA)’s Residential Energy Consumption Survey. I looked at what American households use electricity for in a previous article.

You can see how the demand for desalinisation — 1450 kWh — stacks up against other household power users in the chart below. Note that this is based on the average across the US, and is the electricity for households that have that given technology or end use. So, it shows the average electricity use of a family with an electric vehicle.4

As you can see, it would use a decent — but not crazy — amount of electricity. In the US, it’s on a similar level to many other important technologies like dehumidification; and much less than the energy used to heat water, or to heat or cool their home.

 

But for households in poorer countries, 1450 kWh is a lot of electricity.5 More than an entire family in lower-income countries would use in total. Granted, households in the US use a lot more water than those in more water and energy-constrained settings would.

In the chart below I’ve compared total electricity demand per capita for all uses in many lower-income countries (and those on slightly higher incomes, such as India) to desalinisation of US levels of water consumption, and the WHO’s minimum guideline of 50 litres per person per day.

Providing 50 litres per person per day — the WHO minimum — would need 64 kWh of electricity. That’s about equal to what the average Malawian uses for everything today. Even for those that use more than 64 kWh, electricity demand for desalinisation would be equal to a 50% increase in demand, or more. Achieving American levels of water usage would be unattainable.

To me, the main message of this chart is not that desalinisation is incredibly energy-intensive. It’s that many people in the world still live in dire energy poverty.

 

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Energy demand to supply clean drinking water for everyone

 

Only a fraction of the domestic water we use is for drinking. Guidelines often recommend drinking 2 to 2.5 litres of water per day. There is some nuance to this number, which I’ll leave in the footnote, but let’s take that as a rough estimate.6 We’ll be generous and assume that there are some spillages, so everyone needs 3 litres per day.

If we were to use desalinisation to provide this water for everyone — 8 billion of us — how much electricity would we need?

31 TWh of electricity per year.7 The world currently produces around 30,000 TWh of electricity per year, so our demand would increase by 0.1%. Not a lot!

Of course, not everyone in the world would need drinking water from desalinisation, but you can then quickly slice the numbers. Imagine an incredibly catastrophic and extreme drought left one-third of the world without water: around 10 TWh would be needed per year to provide the most basic drinking water supplies.

The WHO has a guideline that people should have a minimum of 50 litres per day to meet all of their domestic needs, which is not just drinking water but also cleaning, showering etc. As we saw earlier, people in richer countries use far more than this: in the UK, three times as much, and in the US, six times.

If we were to provide the 50-litre minimum for 8 billion people, we’d need 511 TWh of electricity. That’s 1.7% of what the world currently produces.

See the chart below.

 

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What would desalinisation cost?

 

Here I’m focusing on the unit cost. Large-scale desalinisation plants would also need significant capital investment, which will probably be the biggest barrier in many countries. It’s not dissimilar to some renewable projects: the cost per unit of electricity is often very low, but people or communities still need to find the capital up-front.

I’ve tried to find a range of projects across the world that would give insight into how much desalinisation costs, and how this might vary. Most quoted figures are in the range of $1 to $2.50 per cubic metre. I couldn’t find many estimates higher than this. 

There are also some more optimistic figures: the Sorek B plant in Israel, for example, is contracted to produce water at $0.41 per cubic metre. A study looking at 107 desalinisation plants found a minimum cost of $0.27.8

One way to stress-test these figures is to estimate how much the electricity alone would cost. Electricity in the US in 2023 cost around $0.13 per kWh (industry is subsidised, so it sells at around $0.09 per kWh). If it takes 3.5 kWh to produce one cubic metre of water, then it costs $0.45 per m³. Electricity prices in states like California are much higher — roughly twice the national average — so there it could cost $0.90 per m³.

Energy is just one part of the full cost; estimates are around one-third. Multiply by three, and we get around $1.50 per m³. In states like California, the energy cost might be $0.50 higher, bringing the total to $2.

Let’s put these numbers into context. How much would desalinated water cost per person per year?

If the average person in the United States uses 310 litres of water per day for domestic uses, it would cost them $0.42 per day.9 Or $154 per year.

In the UK, it would be similar: $0.43 per day, and $159 per year. British electricity is more expensive, but we also use less water so the costs balance out.

To get the WHO’s “minimum” domestic supply of 50 litres per day would cost around $0.11 per day and $38 per year.10

Here’s the surprising figure. Producing enough drinking water for someone — assuming 3 litres per day — costs just $2.30 for the entire year. That’s less than the cost of a single bottle of water in many countries.

This was far cheaper than I’d have guessed, and in a water crisis I would agree that this is “absurdly cheap”. More expensive than many of us get from the tap today, but pretty cheap for an essential resource.

 

Again it’s worth putting the $38 that would be needed to meet the WHO’s minimum guidelines of 50 litres per day, into context for the world’s poorest.

Some people still live on as little as $2 per day. Getting 50 litres of domestic water per day from desalinisation would eat up more than half of a month’s income every year.11

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Using desalinated water for agriculture

 

Farming is where the costs of desalinisation start to get unfeasible.12

Most of the world’s freshwater withdrawals — around 70% — are used for agriculture. In some countries — particularly in the tropics and subtropics — this can be more than 90%. Making sure that people have drinking water and basic supplies at home is crucial during periods of water scarcity. But when suffer from drought, it’s usually because crops fail and food supplies run out.

Let’s look at how much freshwater is withdrawn from aquifers for agriculture across different countries, and how much electricity would be needed to replace that with desalinisation.13 Note that this is not all of the water used in agriculture, since a lot of it is rainfed.

As you can see, desalinisation to replace just a subset of water used for agriculture would increase electricity demand by around 50% to two-thirds for many countries. For some — often the countries where water stress is already high — total electricity generation would need to more than double. Current desalinisation technologies are not going to be the agricultural safety net for large-scale national droughts.

 

But the bigger constraint for desalinisation in farming is cost. Using desalinated water would either bankrupt the farmer or make food much more expensive.

Let’s take an example of wheat. It takes around 650 litres to produce one kilogram of wheat.14 It would take around 2.3 kWh of electricity to produce the water for this. Take electricity costs in the UK and the water costs $0.66.

The current market price for wheat is around $0.22 per kilogram. The water would be three times as expensive as the current final product.

For maize production in the US, I estimate that desalinated water would cost $0.20 per kilogram.15 In some states with higher electricity prices, it could be double. The market price for corn is around $0.20.

The economics for staple crops that are cheap and have low margins just don’t work.

It might just be economic in fringe cases for high-value crops, grown in conditions that are much more water-efficient — such as indoor farming — but we’re still pretty far from having solutions that could make a big dent in meeting water demand for staple crops.

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Pledge your support

1

He also mentioned this on the Bill Maher show. And at the World Water Forum.

2

Reverse osmosis uses around 2.5 to 3.5 kWh per cubic metre. Thermal technologies can use somewhere in the range of 13 kWh.

3

The average American household uses 1135 litres per day. To desalinate this takes [1135L * 0.0035 kWh] = 4 kWh per day. That’s 1450 kWh per year.

4

Since most households don’t (yet) have an electric car, the actual average across the population would be very low, since most households will use zero electricity for this purpose.

 

5

This reminds me of Todd Moss’s comparison that the electricity consumption of one typical fridge is higher than the total electricity demand of many people in lower-income countries.

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Why ‘The Fridge’ Continues to Resonate

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2 years ago · 21 likes · 2 comments · Todd Moss

 

6

This recommendation doesn’t take into account that you also consume water through the food you eat.

It also doesn’t necessarily need to be in the form of water. Juice, tea and other liquids also count.

It will obviously also vary depending on factors such as climate (you’ll need more in warmer climates if you sweat), your size, and activity levels.

https://www.bbc.com/future/article/20190403-how-much-water-should-you-drink-a-day

 

7

We calculate this as follows: [3 litres * 8 billion people * 0.0035kWh = 84 billion kWh per day]. That’s 31 billion kWh per year. Or, 31 terawatt-hours (TWh).

8

https://www.sciencedirect.com/science/article/pii/S0011916420313114

https://www.sciencedirect.com/science/article/pii/S0957582022009594

 

9

Here we’re assuming that electricity costs $0.13 per kWh. And that the total cost of desalinisation is three times as expensive.

 

10

Here I’m assuming electricity costs of $0.22 per kWh. This is more expensive than prices in countries like the US or China, but lower than rates in many countries in Europe.

 

11

If they earn $2 per day, then $38 would be equivalent to around 19 days of income.

 

12

Here I’m focusing on outdoor field farming, not indoor farming technologies.

 

13

This data is not widely available, nor is it up-to-date. I’ve used data from the FAO’s Aquastat, but for some countries, the most recent year is 2010.

I’m assuming it takes 3.5 kWh per cubic metre.

Electricity generation data comes from Ember (2024) – shown here.

 

14

This is freshwater withdrawals only, so the total footprint might be even higher.