YOu might also want to post this on plumbing. I had a question on whole house water softening systems and got referred over to there. Very helpful...

First you have to decide why you need a filtration system. Do you have city water that just doesn't taste good or is there a health issue with your water. We put in a reverse osmosis system (just for drinking and cooking water) and I really like it. It was through Culligan but there are others. However, not every faucet will accept a reverse osmosis system.

I don't believe there is any health issue here in the
san francisco bay area. It's mostly for taste.
We're in the planning stages now, so there can be
a separate faucet for the drinking water.

Here is my experience on using filters. I have always used the Seagull cold water filter from General Ecology---great filters apparently, they have their own site on the web. I have had two units from them in my last two houses: the first was a cold water only unit with a separate cold water dispenser spout on the counter and the tank under the sink. The second was a filter under the sink that hooked up to the cold water line for my regular faucet, so all the cold water was filtered.
For my next house, I am going with a third option: the same under the sink filter that will filter both the cold water from the faucet AND using the included t-split thingie that comes with the Seagull filter, I'll run a second line over to the InSinkErator hot water dispenser so that all of the hot water out of that separate hot water faucet will be filtered as well.
Does that make sense? Hope this helps!

Here is a link that might be useful: General Ecology water filters

I live in Monterey, and our water tastes disgusting and smells like dirty socks. You have tasty Hetch-Hetchy water up in SF. I don't think I'd even use a filter if I were you. For sure, you don't need the reverse osmosis filter that I have. For any one else's benefit, you need a faucet with an air gap in order to use a reverse osmosis system. I do love the Instant Hot. I have an old one that I am replacing, so I don't have any experience to recommend anything yet. I have looked at Everpure/Everhot and Waterstone.

Someone (ok, salesman trying to sell me on separate insta hot/cold filtered water dispenser) told me that if we do a filter on the main kitchen faucet, it greatly reduces water pressure (thus making the second faucet/insta hot/cold filtered dispenser more appealing - but it seems quite expensive at close to $1000!?). Anyone know if there is any truth to that? I'd prefer to just go with one faucet and skip and insta hot/cold filtered if I can. And our fridge will not have water.

In our last remodel, we installed the Everpure hot/cold faucet in addition to our existing Rainsoft reverse osmosis. If I recall correctly, I had to purchase the additional air gap piece that installed on top of, which made it taller. That was fine for us, it went with our regular faucet perfectly.

The faucet worked well as instant hot. We did not use a cooler so the cold faucet was just room temp RO water. My only complaints were cost, ease of installation (1st plumber was stumped, but we had the parade of idiots doing our remodel) and the faucet dripped occasionally, we could never get that fixed. Here's picture of the sink area, sorry it's not up close:

Just wanted to clarify...we hooked the hot/cold up to the RO, not added an additional faucet.

I have the same question as well. For those of you that connected your filtered water to your hot water dispenser, was there anything in particular that your plumber did differently to acomplish this connection? My plumber/installation guy highly recommends against connecting the filtered water system to the hot water dispenser. He thinks it will back up into the filtered water system. I e-mailed the manufacter of the hot water system and they say there is no issue. Maybe I need a new plumber? Any ideas what I should be asking the plumber to do?

I'm using the Costco 2-stage water filter and the Quick N'Hot dispenser connected to a hot/cold faucet -- http://www.westbrass.com/decorativeaccessories/popups/D2051.htm

the hot water dispenser - http://wasteking.com/products/hotwater/quickhot.htm

I love our insinkerator brand faucet, insta hot and room temperature water, both are filtered. It comes in a variety of finishes. It's one faucet with 2 levers.

I've read here that ro systems waste a lot of water. Perhaps that isn't the case now? Something to ask your plumber or salesperson about. Yes, our water here in San Jose tastes pretty bad to me, even after living here for over 20 years, since I came from Oregon with very sweet-tasting water.