Steam is not required for MED. Hot water < 100C is adequate.
Many ocean-going vessels already use the waste heat from their engines and MED to make freshwater from seawater.
ORC driving RO seems to be most efficient in some situations <https://www.mdpi.com/1099-4300/17/11/7530>, but MED is a simple, no-moving-parts solution that is also efficient.
I'd love to see if you could use spent nuclear fuel (which is an excellent heat source) to just run one of these things continuously for a couple of decades :-).
Why is taking salt out of sea water such a challenge?
Sure, we can get ~1,000 gallons of drinking water for 3$ via desalination. That works out to a monthly water bill increase of ~45$ for a family of 5. Unfortunately, crops need incredible amounts of water. So, growing corn etc with desalination would case food prices to ~quadruple.
Raising crops and live stock on deserts or other marginal farmland is a huge part of this.
t-tape for instance is widely used commercially for irrigation of high value horticultural crops like strawberries, tomatoes, peppers etc.
also drip systems (with individual emitters, not t-tape) are used commercially in many tree crops (citrus etc).
However for agronomic crops (like corn, wheat, soybeans, alfalfa etc), which occur in mass plantings I'm not aware of any drip applications. Certainly at minimum if drip is used for these crops, it is extremely rare and probably not practical.
To get around this you would need to keep the area underwater and slowly replace your water with sea water. But, at that point you’re better off just farming the ocean which already covers the majority of the earth.
I pay quite a bit more than $3/kgal, and a large fraction of that goes toward funding the SFPUC’s massive infrastructure for bringing Hetch Hetchy water to the Peninsula. A desalination plant would be located on the coast or on the bay and would not require this infrastructure.
As far as I’m concerned, the problem is the capital cost of the plant and the plumbing to safely suck in saltwater and discharge brine and has essentially nothing to do with electricity.
The situation isn’t helped by the fact that, in average and wet years, demand for desalinated water would be nil, since the Hetch Hetchy infrastructure already exists.
As to why this is, a single pipe carrying 1,000x as much water costs no where near 1,000x much per foot. Each home might only need 1/10,000,000 the water, but it’s got to be built for peak demand not average useage. On top of this, people don’t live at sea level, so you need to pump that sea water up before you can use it.
PS: Not to mention most distribution systems leak significantly, that 3$ assumes 100% efficiency at 50% it’s more like 6$.
Wholesale untreated water is 1.02$ per 1,000 gallons. Page 16: ( 0.76 per 748 Gallons delivered). Plus a fixed fee for the size of the pipe (22.67$ for a one inch pipe.)
edit: You’re looking at rate W-24. BAWSCA users seem to pay rate W-25, which is far higher. I don’t know exactly what the difference is.
They buy the water from the neighboring municipality for $3/1,000 gallons, and sell it to the users of the system for $23/1,000 for the first 1,000 gallons.
You soon realise half a gallon is plenty to drink, and you don't really need water for much else.
Nothing to do with electricity? What is this based on? Everything I've read indicates it's a very large cost. For example, this  paper puts electricity's share of costs at 44% vs 37 for fixed costs.
The rain that falls from the sky is salt-free, right? It then becomes salty when it touches the ocean?
My roof surface area to consumption ratio is such that this system works pretty well for me (big roof, small human). However with a farm the roof surface area to consumption ratio is flipped - big fields needing water and little to no roof (maybe a tool shed or garage). And you can’t increase roof surface area since that would block sun from the plants. Industrial uses also have a poor ratio. Dense usage of water in a limited size building.
But that’s a lot of shipping. And I wonder if a better way is to capture the glacier melt runoff from Greenland before it can enter the ocean currents, and desalinate that brackish water. I’m not sure what the ratio of brine to fresh water is (ratio of boats in each direction) or the desal versus shipping costs.
Not sure what progress has been made since
The products don't look too valuable, it produce calcium chloride and sodium bicarbonate. How big is the market for them? How expensive are them? Why is no one using this process to produce them using salt form a saline? Where they going to dispose the excess of calcium chloride and sodium bicarbonate that nobody wants to buy?
It looks like a mix of buzzword, like "carbon sequestration" and "brine reduction", but the whole idea makes no sense.
 How much CO2 release the production of CaO? It is not only important to consider the energy to produce the CaO, but also that most CaO is produced from limestone that is CaCO3 in the reaction CaCO3-->CaO+CO2.
> Ecological impact
The amount of salt that goes to the region's soil and rivers is enormous. The Werra river has become so salty (up to 2.5 g/L chloride ions, which is saltier than parts of the Baltic Sea) that few freshwater organisms can survive in it. The groundwater has become salty as well. K+S are licensed to keep dumping salt at the facility until 2030.
100s of millions of years old sea salt for cooking from the Iapetus Ocean.
Putting it back would kill ocean life in the area.
Edit: To put it more generally: To avoid https://en.wikipedia.org/wiki/Salting_the_earth
> Other methods [of disposing of brine] include drying in evaporation ponds, injecting to deep wells, and storing and reusing the brine for irrigation, de-icing or dust control purposes.