I see “reverse osmosis water” on a lot of products these days and I’m curious how reverse osmosis is different.
Lithuim: In osmosis, water travels through a membrane from a low-concentration (i.e. less dissolved solids) mixture to a high-concentration mixture until the concentration on both sides is the same.
This happens spontaneously and can be quite dramatic if one side is extremely highly concentrated. This is why drinking salt water is so harmful, osmotic pressure starts sucking water out of your cells.
*Reverse* osmosis is the inverse process, forcing water to cross from the concentrated side to the pure side. This *won’t* happen naturally and requires high pressures, but also acts as a very effective filtration process because the membrane excludes most particulates and large ions.
Johan_NO: I don’t get how “reverse osmosis” is any different from “filtration”???
baggier: Just to confuse the issue – it is possible to purify water through forward osmosis as well and there are plants that do it. One typically draws the (pure) water into a another medium (say an amine) and free the water through another step – maybe distillation or reverse osmosis
cardboardunderwear: Osmosis is when a liquid (usually water) is flowing through a selective membrane from a lower concentration solution to a higher concentration solution.
So in the example of salt water. If you have a strong salt water solution on one side of the membrane and a weak solution on the other side, the water (but not the salt) from the weak side will flow across the membrane and dilute the strong side until the concentration of the solution is the same on both sides.
Reverse osmosis is increasing the pressure on the higher concentration side to force the water to flow from higher concentration to lower concentration which has the effect of purifying the water.
In order to increase that pressure you have to use a pump which takes energy (read: money) to run.
Mikejl1719: When a liquid gets osmosisized, it literally goes through a liquid diffusion process. Think about it, when you put ice into a thermos, you get condensation right? The insulation in that thermos becomes exothermic, resulting in that condensation. Now put that same amount of ice into that same thermos while in a oven? You guessed it, reverse exothermic reaction. The volume of that melted ice will literally increase. Don’t try this at home lol.
With Deer Park and Aquafina (maybe Nestle water as well but not sure), they have gigantic reverse exothermic diffusion furnaces. Thousands of plastic bottles are grouped together and ” staged ” but only by 5 groups at a time, multiply that by hundreds of furnaces and that’s how you get your delicious reverse osmosisized water.
This process has been shown to be drastically cheaper than filtered mountain springs water. Which is pretty much why you can buy 25 bottles or so in a pack for only 3 bucks. It costs jobs unfortunately, but we’ll save the politics for a different ELI5.
Source: used to work as a lead operator in a Deere Park factory.