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RO/DI unit opinions...

The system you are looking at is very much like the one I use if it includes all the listed parts (it is unclear to me if they are options or included in the price, I paid about $30 more over 2 years ago - also eBay).

I can't help with choice but I will warn you that regardless of the GPD promised, you will be lucky to get 24 GPD (i.e. roughly a gallon an hour) out of any system using normal 60 psi (when our water pressure is lower it takes 3 hours to fill my 2 gallon buckets). It is my understanding that when you replace the RO filter you do have to stay with the same GPD rating but I have no idea why. The only way to get more water through the system will be to add pressure via a pump to the input side. This is NOT to make you rethink any purchase, I would be lost without my RO/DI unit, but to forwarn you of the small print. One way you might eliminate vendors is to email them and ask what GPD you can expect at normal household pressure. The answers you get might give you a confidence rating but I expect there is little difference in the systems. I would suggest a TDS (total desolved solids) meter as well to help know when you need to change your filters. I found a great one on eBay that I keep inline and can test both my incoming and result water (needs to be hooked up before the DI resin output).

The RO only tap has some advantages (comes with this system - the faucets are connected this way as DI water is NOT for drinking). The DI portion (takes out minerals/metals) is a sand type resin filter. It will need replacing and comes in a both a clear refillable and disposable cannister. This system has the refillable kind but you can always replace it with the disposable (I use the refillable canister but it is hard to pack properly.

I have the back flush valve on my unit and it does seem to help keep the membrane functioning longer (more gallonage) than its rating. They show this in the parts list but it is not listed in the inclusions.

I would highly recommend getting a storage tank as well (again part of what you are considering). With a 4 gallon tank you will have about 2 gallons of water on demand, otherwise it is a looooong wait. You can fill a large plastic bucket to keep a reserve. I use a shutoff float in a 14 gallon to mix my saltwater but don't have a second bucket with shutoff for top-off fresh and need to do something to increase my freshwater reserve. I am considering adding a piggy back RO (I have multiple tanks) to my system but don't know of anyone who has done this so maybe Thales/Paradox will chime in here and enlighten me on the advisability. My alternate would be to add a second unit in the kitchen ...

You might also shop eBay (way cheaper) for a couple of sets of replacement carbon and filliment filters. You can buy them at Home Depot for over twice the price but I find that by keeping a case on hand I am not only saving money but I change out my filters regularly. Additionally, I would recommend that the first cannister be CLEAR. It will be the larger particulate filter and you can visually inspect it (the carbon filters don't need the clear housing because you really can't tell much by looking at them but the first filter is white and shows discoloration).

One other nicety is color coded tubing. It is not a biggy but helps with both the installation and determining what hose is what later.
whew!!! thanks Dwhatley!! I will be reading this numerous times before and in the process of getting one- Lots of great information!!
Glad that tomb was of use. I was totally overwhelmed when I purchased mine and made Neal set it up but once we understood the plumbing (the colored tubes really do help with the comprehension) it seems really simple. The weird part will be plumbing (and understanding) how the holding tank works. The mind just refuses to grasp a one lane two way street. The secret is in the pressurized tank but it just "feels" strange when you set it up. I put together some pictures of my set up for someone else a while back. If you PM or email me with your email address, I will send them. I an not sure it will help but I went through the effort to create the pictures so you are welcomed to them.
I also bought an RO/DI unit from ebay for about $100 a couple months ago. it's an off-brand from a manufacturer called "abundant flow" but it seems to work fine.

it claims to produce 100 gallons in a day, but i'd estimate more like 60 or 80 if i ran it continuously for 24 hours. Which is still fine for stockpiling pure water for topoff and weekly changes. i store the pure water in a 20 gal. rubbermaid container with a powerhead and an air pump running in it. a day or two before i do a water change i mix a batch of saltwater.

when the unit came from ebay, i was definitely confused and overwhelmed. it's a really high-tech looking device and it came with sparse instructions. in practice, though, it's really simple to use. a red tube screws onto your sink faucet (input), a yellow tube goes down the sink drain (waste water) and a blue tube goes in your collection bucket (pure water). it takes about 5-6 hours to fill the 20G container, and i produce about twice as much "waste water" as "pure water." I just set it up and let it run, and try not to monopolize the sink from my 4 roommates for longer than i have to!

just make sure you order it with the right input adapter. mine came with an adapter for a garden hose, rathern than a sink faucet and i had to order the right piece separately. Oh and the valve system was very confusing also. there are two ballvalves on my unit and i just flipped them on and off in different combinations until i was getting 2x waste water and 1x pure water like i knew i was supposed to.

the filtration tubes are all replaceable on my unit and you can order backups from the company's website. (Water Softeners, Iron Filters, RO Systems - Afwfilters.com). when i emailed them about my adapter problem they actually responded right away, so i guess i would recommend this manufacturer to others.

generally, look for a 3-stage unit (you really don't need more) that advertises around 100 GPD. that should be sufficient.

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