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Battery-free solar desalination system produces up to 5,000 liters of water per day
(alpha.leofinance.io)
this post was submitted on 03 Jun 2025
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Approx 35 grams of salt per litte. 35 g x 5000 litres per day is about 385 pounds of salt everyday. This is the problem with desalination no one discusses.
On the low end people use around 300 litres a day. So this is only enough water for 16 people. When you start scaling this it really becomes clear.
Let's say you wanted to provide LA with water from desalination. At around 23 pounds of salt from 300 liters of water per person with LA population being 3.8 million that would make 87 million pounds of salt... wait for it... per day!
Sure you can put it back into the ocean, but that is not good for sea life at all. Not to mention all the energy needed to pump it back if that is what you choose to do. I don't think sequestering is an option either.
If you have a conveniently located valley you're not using, you can make a new great salt lake for a few years. 87 million pounds of salt sounds like a lot, but a cubic mile of salt weighs approximately 9 trillion metric tons, or about 20 quadrillion pounds, or over 600 years of salt at 87 million pounds per day.
I'm sure there are a few people (very few) who would disagree, but a quick glance at a topo map shows Shelter Valley as a possible target for a strategic sea salt reserve deposit that could serve the area for hundreds, perhaps thousands of years. San Francisco bay looks like they have salt ponds in what could otherwise be valuable real-estate.
I think it is important to keep in mind how much energy moving 87 million pounds of salt a day would take. Unless this valley was extremely close it would be prohibitive.
I do think you have a decent idea though if we had to use desalination and didn't want to dump it right back into the ocean.
The real answer is to dilute the salt back into the ocean, but even the cost of transport - whether by truck or rail or pipeline - a hundred miles and +3000' of elevation is likely less than building and maintaining a system that distributes that salt widely enough in the ocean to have negligible ecological impact at the points of dispersal.
A thousand smaller desalination plants spread along a hundred miles of coastline each distributing 87 thousand pounds of salt per day (basically: one pound per second) would be more feasible for ocean discharge than anything you might try to do from a single point. The system would also be much more robust / less prone to critical failures. ~10% of the plants might be offline at any given time while still providing full required capacity.
Looking at those numbers, I would propose something like 500 plants, no two closer than 1000' from each other along the coastline, each distributing up to three pounds of salt per second in a 6" outflow pipe at least 500' offshore that's carrying 100 gallons per minute of water with that salt dissolved therein. The discharge could be through a series of 100 1" holes spread 1' apart. I'm sure there would be local ecological effects, but in most areas they should be minimal by the time you're 200' or more down-current from the outflow.
Compared to treated wastewater discharge, I think the salty water discharge would be much less impactful. There's probably some opportunity to combine treated wastewater with the salty discharge to further treat the wastewater, though I wouldn't want to do that in ALL the salt discharge plants (you'd want some to study the salt impact alone.)