[whoisburbansky]

Wait, where do the other two units of water go?

[kibwen]

Ideally into your sewage system, as they are now concentrated wastewater (although if you live in a developed region with centralized water treatment, there won't be that much waste in the water to begin with). RO systems designed for processing seawater have a much harder time of it, as their waste is ultra-salty brine which will kill any local marine ecosystems if you decide to just dump it back into the sea.

[kurthr]

Since the flow of deionized water is only 1/10 of total water flow... I think the increase in "waste" concentration is also only about 10% even of the filtered water is perfectly pure. So if you had 400ppm total dissolved solids it would now be *10/9=444ppm. Not much of a concern.

[seanp2k2]

Seems like thie brine from desalination plants should be pumped into tailing ponds and dried out to get useful minerals out of it that could then be sold to help offset the cost and environmental impact of desalination. https://news.mit.edu/2019/brine-desalianation-waste-sodium-h... looks like this is not an original idea :)

[gnicholas]

That would not be ideal for me (Bay Area resident) where water is crazy expensive. I'd want to keep it for watering plants, flushing toilets, etc.

[vl]

Essentially you can think about them as "water which washes the filter", i.e. contaminants removed from the drinkable water are in this waste stream. Without this filter this fine would clog up in couple days. In typical home install this water is just dumped into the sewer, if you have use for gray water, you can capture it and re-use it.

[r00fus]

This wastewater isn't even gray water, it could be simply reused as non-potable. I think of it as "light gray water" - you wouldn't want to drink it but it would be better than gray water for plants, etc.

[bradleyhd]

They’re usually discarded into the drain line, so into the sewer system

[Arrath]

God, what a waste.

[spookthesunset]

Can’t they be used as a source of non-potable water? Like toilets, irrigation, maybe laundry?

[rollcat]

Sure. I've lived on the countryside as a kid, it was before the village had a sewage system built. We not only had RO, but also a tiny waste water processing plant in the backyard, you'd put a spoonful of some powder in the tank once a month or so, and the "cleaned up" grey water would slowly trickle out and irrigate the vegetables in the garden. This was around 2002. I'd like to live like that one day again.