Reading the article might help:

> Unlike some desalination systems, there is no accumulation of salt or concentrated brines to be disposed of. In a free-floating configuration, any salt that accumulates during the day would simply be carried back out at night through the wicking material and back into the seawater, according to the researchers.

Your rely is not helpful. The problem with any desalination system is that it creates brine. And brine in large amounts is toxic to the marine environment.

The only difference with this example is its small scale. Once it is scaled up it will have the same problem as any existing desalinating plant.

But you would never scale this system up - it's entirely inefficient compared to reverse osmosis, on a cost basis. This is the type of system that you would use for just a few people, and as such - brine would never be an issue.

Yes. So it is not an issue for the device. However, the salt does end up back in the ocean where at scale the salt levels will be higher leading to the (edit: local) environmental issues mentioned by the GP.

The sea is a big place. I could imagine perhaps some very localised effects near the plant, but even this isn't obvious.

> imagine > perhaps > but even this isn't obvious

So basically you're admitting you don't know anything about the subject, but you're making a conclusion anyway. It's OK to admit you don't know enough about a subject, and it's OK to not comment or theorize based on no knowledge besides an imagination.

A man once said, "imagination is more important than knowledge."

That man's name? Albert Einstein.

I didn’t know that making assumptions while clearly saying you are making assumptions is forbidden on HN.

Is the water cycle not a thing any more?

Not an expert but I could imagine some local negative effects. Salt concentration may get higher in the area where the brine is returned. Depending on volume, currents, etc...

A large part of the fresh water generated may be used for watering crops or gardens, and would thus evaporate in part. The evaporated water in desert areas would probably rain back down far way, and take long to mix with the sea near the plant again. For example, the Red Sea has much higher salinity that other oceans due to high evaporation and narrow connections to the other oceans. I doubt the effect is large though.

Indeed - the dead sea has stupid high salinity because the only way water leaves is via evaporation :)

It is a very odd sensation to "swim" in the dead sea. Even floating is pretty hard because you are so buoyant. It's probably the closes to true weightlessness I will ever get.

It makes no difference how concentrated the output brine is if it's the diluted to same concentration at the outlet and the same amount of fresh water is extracted.

You completely miss the point. Extracting fresh water from salt water creates brine and in a large scale plant it is extremely difficult to dilute it sufficiently.

The only answer is to pipe the brine into areas with strong currents, or dilute it by distributing it over a very large area.

Brine is the biggest issue with some desalinators, not this one.

Power can be a constraint, too. It depends on how much power you have available or can pay for, how much fresh water you need and how pure, how much you can buffer, etc. In short, power/cost is a constraint sometimes.

This doesn’t use electricity at all, the “solar power” is heat from the sun causing the water to evaporate. It’s a still, not a filter. According to the article the salt/brine freely flows back into the body of water.

Which by definition will increase the salinity in the local environment.

The article directly addresses your point.

It doesn't. Any salt extraction creates brine which must be disposed of somehow.

The trick is to flow seawater past the still and take only, say, 1% of the water from each litre that flows past, which you can do with a still as opposed to a filter.

It's a bit like slingshotting a space probe past venus. Technically to move Venus a bit closer to the sun, but not enough to make a difference.