A permeate pump can typically reduce water waste in reverse osmosis systems by up to 80%. In general, permeate pumps can achieve a waste water reduction of around 50% to 80%. This means that for every gallon of purified water produced, only around 20% to 50% is wasted as reject water. This is achieved by utilizing the energy from the brine flow to enhance the pressure applied to the feed water, leading to increased permeate production and reduced reject water volume. Typically, these pumps range from $50 to $200 and they do not use electricity.

The elevated pressure allows for more effective filtration and higher water recovery rates. By boosting the pressure, permeate pumps facilitate a greater volume of water passing through the semi-permeable membrane, resulting in increased production of purified water (permeate) and reduced reject water (brine). The heightened pressure helps overcome osmotic pressure and allows for a more thorough extraction of purified water from the feed stream.

The domestic RO systems put pressure on the clean water output and don't have recovery systems for brine pressure? What? My only experience with RO systems are on sailboats, where a brine pressure recovery system is the only way to get the power down, and the water trickles into the tank under low pressure from where it is pumped out.

The linked system above just sends the unfiltered tap water down the drain. I have had two iterations of the GE system and it says so in the manual, for instance. I am not sure about other brands and their systems.

Most in-home systems sold today drain to waste without any attempt at recovery to keep manufacturing costs low.

They don't boost the feed pressure, just isolate the output permeate line from the back pressure of the storage tank. Instead of the membrane output pushing against the increasing pressure of tank as it fills (decreasing output) it produces into a void in pump body which the pump periodically pushes into the tank from spring mechanism wound by the output waste water.

They work pretty well to reduce waste but do add complexity to what is already a somewhat complicated device under the sink. They will also create bad TDS creep if used without an auto-shutoff valve installed in the RO.

Yeah my dad has an RO system at their house but it goes to a special tap next to the main one that is used only for drinking water, due to the waste associated. Maybe it isn’t needed for hand washing, showers, etc as long as there are good standards at the water distribution facility.

Thats how I use it. In theory the waste could be used for irrigation or mixed into shower water but that requires more plumbing to deal with an external cost (in areas where water is limited).

Well, if you live somewhere with a municipal water supply, the water just gets recycled anyway. I suppose if you’re on septic it’s still going right back into the ground it came from.

Drinking water is probably such a small percent of overall water use that wasting even a multiple of it doesn’t amount to much anyway.

So filter away! I’ll worry about my r/o waste when people stop diverting rivers to grow almonds in the desert and not a second before.

I think the point is that we should not as a general rule recommend people do RO for their entire house. Toilets, showers, and washing machines don’t need RO water and if a lot of people did a whole home RO system we would start to see waste add up.

Oh. Sure. That will always be so cumbersome we don't have to worry about it. That would be a huge RO system. They don't have a lot of throughput so you'd need a big storage tank or a very large set of filters and a pump I'd think. I'm not at all concerned whole home RO will every be common.

Only places I’ve seen it are places like China where people just don’t trust the water at all.

A friend of mine in Brazil had a whole home filtration system (not RO) that even had a UV sterilizer at the end!

We live in a water supply area with water one order of magnitude harder than anywhere else in our county.

I'm putting an RO unit in our kitchen to serve drinking and dishwasher needs. Our dishwasher needs descaling after a couple of months of normal use. Other uses (shower, toilets) aren't impacted by our super-hard water, so no RO for the whole house, mainly because of the water waste you note.

A big issue is returning it to the ground doesn't mean it reenters the aquafer you might be drawing from if you're on a well system. It happens all over the place and especially in California, the aquafers aren't replenished well by ground water (and the extreme pumping causes the aquafer to compress permanently losing water capacity).

But again that’s entirely because of agricultural and industrial use. There’s plenty of water for homes, there’s not plenty of water for homes and mass farming in a desert.

This is the exact line of thought the people who use the water want to encourage. They want you to worry about your water use so you don’t worry about theirs.

Anyone considered just sending the brine to the yard as gray water?

Premiere H2O has a system that dumped the water into the hot water line, similar to a hot water loop, but in reverse. There’s a lot of caveats with that arrangement (doesn’t really work with a tankless water heater, for example).

Wait, they push the waste/brine into the hot water line? Wouldn't that defeat the purpose of filtration?

I was thinking more of using it typical gray water usage like watering plants.

I imagine despite the term brine it is still incredibly clean water

> Wait, they push the waste/brine into the hot water line? Wouldn't that defeat the purpose of filtration?

Hot water is for external use only.

... you’ve never used hot water to fill up, say, a pot of water for cooking?

it's gross. Don't do that.

You still absorb an astounding amount of chemicals through your skin.

When you say brine is that in seawater desalination RO or are you using that to include non-seawater RO reject water?

You could definitely use it as gray water but if you are filtering for contaminants, that water would have a higher concentration and if you were pushing it out as gray water, would those areas of the yard have higher levels potentially of contaminants?

It seems like it would be mostly irrelevant that it’s not efficient?

What percentage of residential water goes to drinking water? I think of all water use in aggregate, in many places it’s already 90% is agriculture and 10% residential. And of residential you probably waste more water in a single toilet flush than you drink in an entire day.

I have an RO system, which seemed great until I realized the nicely filtered water runs through plastic tubing before coming out the faucet.