Pretty much if you're on a municipal water system, your tap water should already be clean of microbes and things like that. The 2 things you generally pick up are maybe some rust taste from the pipes, and chlorine that they put in your water to kill the bacteria.
I don't know exactly where, as I've never bothered to do it, but there's a place online I believe that you can look up the water company in your area, and see what kind of 'stuff' is in your water.
Assuming you're on a municipal system with "clean" water that just doesn't taste great, than you don't really need a high end filter system. You don't need to filter out .003 micron stuff if there's already none in your water!
Reverse Osmosis systems, in particular, are very wasteful for home use. From Wikipedia:
Household Reverse osmosis units use a lot of water because they have low back pressure. As a result, they recover only 5 to 15 percent of the water entering the system. The remainder is discharged as waste water. Because waste water carries with it the rejected contaminants, methods to re-cover this water are not practical for household systems. Waste water is typically connected to the house drains and will add to the load on the household septic system. An RO unit delivering 5 gallons of treated water per day may discharge 40 to 90 gallons of waste water per day to the septic system.
We wanted to improve the taste of our water, and wanted the convenience of having the filter at the tap, not having to refill a pitcher, etc. -- but we didn't want to put out the $$$ to install or maintain a Reverse Osmosis system.
We put in this
Filtrete Advanced Water Filtration System from Lowes. It's basically like a big Brita filter that just attaches directly to the faucet. You
could use it with a
filter faucet as well, but for now we are not.
So the way it works is just to filter 100% of the cold water coming to whatever faucet you attach it to -- generally the kitchen faucet. We have not noticed a significant reduction in the water-flow through that faucet, but it's only been about a month -- so time will tell.
Wanted to improve the taste of the Ice in the freezer, so we installed an
inline ice-maker filter as well.
For the one under the sink, you just twist in a new cartridge every 6 months for $20. The one behind the fridge says it can go for a year, and it's about $11 to replace. So for about $101 the first year, and $51 every year after that, we are able to filter all our culinary water.
I know Flashaholics tend to be gadget-a-holics, but it's worth figuring out what you need to filter out from your water, and then buying the right tool for the job (As opposed to buying more filter than you really need). The filter we are using goes down to 9 microns, I believe. Ours is the "Advanced" model, and there's one called "Professional" that goes down to 5 microns. Well we don't need to filter down to 5 microns, so we skipped that model...a savings of about $10 every time we need to replace the cartridge. Both the "professional" and "advanced" models use the same "docking station" however, to connect to the faucet. So if we wanted to upgrade our filtration at some point...we could by simply upgrading the filter.