Unrelated, but which brand did you settle on?

The plastic tubing is the best way to install. This ensures ease of install and allows you to pull the filter housing to make it easier to replace filter cartridges(which should be replaced every 6 months), without disconnecting any plumbing. The fittings are very reliable.

Plastic tubing and the connectors have gotten better over the years, so they are not a big problem. I would swap the saddle valve for an angle stop valve.

For ease of filter changing, I would put the unit in the basement if you have one, rather than trying to work under a sink.

I would put a "T" in the output line and feed the refrigerator purified water, in addition to the new small faucet. You can still plumb the frig with copper if you want, the big boxes sell all the adapters you'll need to switch better copper and plastic or vice versa. They also have additional tubing if you decide to locate the filter away from the sink.

If anything, you may want to find a better small faucet, the RO units I've seen all come with a cheap plastic faucet.

Thank you for the responses. Okay I'm hearing that the plastic tubing is okay. At least it's only under the sink and it's where I can see it, not threaded through behind the cabinets to the refrigerator or something like that. Correct me if I'm wrong, but isn't the full house PSI (~70 for us I think) pushing full time against the plastic and the fittings?

homebound: I'm not sure if I'm understanding your question correctly, but if I am let me explain this way. I researched and discovered that many "name brand" water filter systems (I'm not talking about RO) use proprietary sized filter cartridges. That means you get to pay a lot because you have to buy "their" water filter cartridge. I discovered that their are generic standards, such as 10" which seems to be very common. You then just get one or two or three (depending upon how many stages you want) standard 10" filter housings and then you can choose from a plethora of 9 3/4" or 9 7/8" filters that range from about $3 to $25 or more. So the whole "system" costs less and the filters cost less. Competition is good!

Chris8796: Thanks for the good advice. I think I read one of your posts already on this. I definitely intend to get a nice (not plastic faucet) as to plumbing it to the refrigerator so as to have only one (cheap) filter...that was my plan. Unfortunately, I didn't tell the contractor and he plumbed a brand new line from under the house to two new locations for me already...oh well. That's why I want to be ready with my filter BEFORE the finish plumbing at least. I had thought I would use the John Guest valves. I've seen those recommended here and elsewhere.

Also, is it true that you tap into the cold water line under the sink BEFORE the shutoff valve to the sink faucets. Wouldn't it make more sense to do it after?

- Jim

You can get an angle stop with two outlets to serve the cold for the kitchen sink and the under sink filter. The shut off will effect both outputs.

I like to use these

John Guest fittings are the bomb and the good ones are tested to over 100psi. Like everything else there are the cheap imitations. Look for a brand name like John Guest or Watts.

If John Guest fittings blow up as you claim, isn't it as good as a cheap immitation?

"If John Guest fittings blow up as you claim, isn't it as good as a cheap imitation?"

Only in Jersey.

Seriously, never had a John Guest or Watts fail and they are too easy to use.

I'm looking for a better way as well. I hooked up the Omni filter in Jan '08, and the connection to the water supply valve seperated in June while I was at a kart race 200 miles away - at 1:00 in the morning. My wife freaked out and could not find the shut off valve due to the volume of water spraying under the sink. She managed to get into the crawl space and shut off the main water valve. I had failed to add the copper insert to the 3/8 plastic line where it attaches to the supply valve. After driving back home and adding the insert, I was confident the problem was resolved. To my dismay, the line seperated again on Feb 13 '09. It must have been running most of the day when my wife came home from work and found water everywhere. I have replaced all the parts again, but fear that after 6 months or so it will come apart again. Surely there must be a better way than plastic line with plastic compression rings.

By "plastic line with plastic compression rings" do you mean screw down compression fittings with inserts and ferrules?

If you do then use the push-in John Guest style. They do not fail.

Also check your static water pressure. If you have a PRV that is goofy or a thermal expansion problem you might be seeing very high pressure at those connectors and their failure might be a symptom of a larger problem.

I install a copper tee on the cold stub out pipe under the sink
then install 2 brass craft angle stops. using 3/8 copper tubing, hook up the filters.using compression fittings
..I know it will be there a long time