2 stage vs. reverse osmosis?

hello, i live in the city in california and i want to put a water purification system in my home.
i've learned that reverse osmosis wastes a lot of water to produce the purified water. i don't understand how this could happen, but it doesn't appeal to me at all.
i'd rather use a basic two stage filter which doesn't seem to waste any water.
BUT, what will be passing through that reverse osmosis would normally take out? i can't seem to find this informaiton, they both seem to have the same list of filtered items.
anybody know? does uv filtration matter in the city?
also, would it be redundant to add a whole house filter, and then a two stage filter under the sink?
thanks, max
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ok, i've found some anwers from the ge web site:
it seems RO systems filter out minerals that regular filters don't catch. among them: arsenic chromium sodium sulfate ammonia nitrate tannins copper magnesium
what does this stuff do to the water? to plants? to people?
also, there are two types of 2stage filters by ge: one reduces: volitile organic compound benzene
and the other reduces: toxaphene 2-4, D
what are the differences between these items. should i use both filters?
the common stuff that all these filters take out are lead,mercury, atrazine, lindane, cysts, asbestos, turbidity, the taste and odor of clorine, sedimenta and rust.
and, anybody know why water is wasted with RO?
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snipped-for-privacy@gmail.com wrote:

I'd suggest you contact your water department for a copy of their annual report / water analysis. Likely most of the stuff the filter would filter isn't in the water to begin with. If you just don't like the chlorine then a charcoal type filter will take care of that pretty well. Unless you have some pretty old water lines in your area you shouldn't have particulate issues, but a whole house sediment type filter is dirt cheap if you do need one.
Pete C.
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Max wrote: and, anybody know why water is wasted with RO?
RO membranes will waste 3 to 4 times as much water as they filter for drinking. The membrane will only allow a certain size molecule to pass, and any compounded water is rejected. You don't have to waste the brine, though. It can be collected for flushing toilets, laundry, and other end uses. Tom
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Correct. Imagine the membrane as a balloon around which water is run. As you said only the pure water molecules can get through the skin of the membrane and thus shuttled to the holding tank. Seems the ratio is 25 gallons of water down the drain for every one gallon to the tank. Used to be worse as the water always kept running but models now shut the water off when the tank is filled. The OP should be aware that it is necessary to run a water softener ahead of the R/O as unsoftened water with it's excess calcium and magnesium will clog the membrane and shorten the life of this very expensive part of the system.
Tom G.
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There is no "THE" ratio, it varies according to the design of the RO system. Mine is (according to the installer) about 2 gallons flushed for every one purified. They had a high end model that was supposed to approach 1:1, but I don't have any need for that, where I am, given that getting rid of water is more of a problem than finding it.
As for UV "Filters", they don't remove anything from the water. They irratiate it with UV light, and any organism that can't withstand that amount of radiation croaks, while any organism that can, happily breeds deeper in your water system, feeding off the corpses of it's dead brethren.
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And I gather that desalinization of sea water works the same way? On one Caribbean island I was recently on the desalinated water from the tap tasted salty.
Don <www.donwiss.com> (e-mail link at home page bottom).
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wrote:

Water is forced through a membrane that rejects most every thing else, the purified water flows to a storage tank while the concentrated 'brine' is flushed down the drain.
R/O actually wastes about 4 gallons for every gallon it produces. It removes substances at the ionic level. It has a 90 to 95% filtration efficiency depending on the filter and the source water. Using a water softener will actually help with the efficiency as an r/o unit has an easier time (no scale buildup for example) filtering sodium rather than calcium.
If the source water has harmful bacteria in it 5 to 10% get through and they can replicate after the filter. If the water has bacterial contamination it will help to have U/V sterilization before the r/o.
You do NOT get a significant amount of calcium and minerals from your tap water in the first place and drinking r/o or distilled water will not harm you from mineral loss.
Deionization strips the minerals from the water but doesn't clean the water at the level of r/o. Ionization resin beds can only be recharged with some rather harsh chemicals. No water waste.
Distilled requires energy to vaporize the water. Some contaminates will pass in distillation but can be removed with carbon filtration. Minor water waste depending on the condenser.
-
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so to avoid wasting water, if i run the brine drain line to places like the waching machine and the toilet and the shower, will there be enough pressure in there? or would it be best to tap it back into the cold water plumbing right before those appliances.
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On 1 Mar 2006 13:01:33 -0800, snipped-for-privacy@gmail.com wrote:

You probably don't want to put back pressure on your drain line. You can save it in a barrel outside for watering the garden.
-
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Max wrote: so to avoid wasting water, if i run the brine drain line to places like the waching machine and the toilet and the shower, will there be enough
pressure in there? or would it be best to tap it back into the cold water plumbing right before those appliances.
The drain from an RO filter flows very slowly. Probably too slow to keep up with a party when there's a line-up of women at the bathroom. They seem to need to flush more, in general. So direct hookup is not gonna work. You need to store the brine somewhere, preferably higher than it's point of use, and from there you can pipe to your toilets/washing machine. Not to a shower or existing waterline, though. And like Adiabatic sez: no back pressure. Tom
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RO reject water is pretty poor quality, you really don't want to use it in appliances or mix it back into 'potable' water but.... to do that, you would need to collect it and then repressurize it, the drain water from a RO is gravity feed and it won't run uphill. Any restriction in the free flow of the reject water will prevent the RO from operating correctly.
If you don't consider watering the lawn, washing veggies or a vehicle as "wasting" water, then the use of a RO for high quality drinking/cooking water is not "wasting" water.
No RO has ever had a 25 gal to 1 ratio; the worst has never been over 5-6 to 1.
Unless you have a proven need for a RO, you are much beter off with a single to 4 stage drinking water filter based on what and how much of it is in your water; if anything worth removing/reducing.
The best place to buy any water treatment equipment is from an independent water treatment dealer. We have any type of disposable cartridge media needed from sediment and carbon to specific anion or cation Nitrate/Nitrite, softening, arsenic, lead etc. resin cartridges. We can also use any of them in a RO; which makes a RO specific to the water it is installed on.
Gary Quality Water Associates
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I'm sure your right in that ratio, however, twenty years ago, when I first started selling them for Sears, we were instructed that the average ratio would be 25 gallons of water wasted for each gallon of purified water used. The reason being that the units we sold then did not stop running water once the reservoir was filled but continued with water going down the drain. A couple of years later, our units would stop the flow of water once the tank was filled. Of course, that may have all been hogwash to get us to promote the more expensive models.
Tom G.
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Gary wrote:snip<the drain water from a RO is gravity feed and it won't run uphill.<snip
Uh, wrong. My brine travels uphill about 6-8 feet, RO still effectively filtering, too.Tom
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tom wrote:

Hmmm. He must have been snoozing in HS biology/chemistry /physics class. Sounds like does not understand what OS means, LOL!
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Tony wrote: Hmmm. He must have been snoozing in HS biology/chemistry /physics class. Sounds like does not understand what OS means, LOL!
Heck, I don't know what OS means, either. You mean OSmosis? The tendency for a thing to go from it's place of most concentration, to it's place of least concentration most rapidly? Man, was I stoned _that_ day. Tom
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Pete C. wrote:

I am on City water. A whole house filter is attached before the first use point inside the house. You would be AMAZED at the quantity of MUD that is in the filter housing when i change it out every six months or so.
City is aware of water system problems and has a two year program to replace leaky mains. The water quality report gives GREAT figures, but it is based on water leaving the water plant, not delivered at a residence.
Filter housings only trap mechanical stuff. Add a carbon block and chlorine is also absorbed.
RO ONLY allows H2O and O2 molecules to pass thru its membrane, and precious little of anything else (>95% rejection of almost everything). There MUST be some water wasted as the membrane needs to be cleared of the waste products. Generally, an RO produces 6-8 gallons of waste for every gallon of product delivered, except in commercial installations where a portion of the waste water is recycled thru the unit.
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