I have had a Whirlpool Ultraease under-sink system for about 3 years now. I can't find the system online anymore, but it's sort of like this
. It consists of two different filters under the sink and a second faucet on the sink (4-hole sink). We have to replace the filters (a 30 second job) once a year or so. It has paid for itself many times over in the amount of bottled water that we haven't purchased.
I *am not* a plumber by any stretch of the imagination, and generally not all that handy around the house. But, I did manage to install it myself, and it wasn't too difficult. It did take me most of a weekend to do, but mainly because I had to re-do most of the water pipes under my kitchen sink because the previous owners had done some strange things with the fittings. It was a PITA (literally!) while doing it, but in hind-sight I did learn a lot.
We do really like the water that it produces. I know that every municipal water supply in the US is safe to drink, including ours. But there's a difference between 'safe' and 'tastes good'. We can really tell a difference between what comes out of the tap and what comes out of this thing. The water it produces is indistinguishable to us from any expensive bottled water. And I'm talking about the good stuff like Evian, Voss, or some of the other expensive ones that claim to come from Iceland or Norway, etc. Very clear, clean, and crisp tasting water. It's really nice. Not a trace of anything else in it. No particles floating around or anything else. Just, water. Unlike the tap water that tends to taste a little 'minerally' or 'treated' to us, and can occasionally look like there are a few particles of *something* floating around in it.
Everyone's water is different though. Maybe these filters are less effective in other places. In the midwest where I live, our water has a fair amount of lime in it. It also has *slightly* elevated nitrate levels (from field runoff, fertilizer, or... poo) than other places. Still *way* below the EPA limits, but it's there. That's clearly stated on the yearly water-quality assessment that I get from my city. So it could be that if you live somewhere away from farmland, your tap water might just be of higher 'tasting' quality. And of course, the source of water itself plays a big role too. Everyone's water comes from different places and contains different minerals and chemicals, depending on the geology and treatment options of your city. As an example, I know that the tap water at my in-laws, who live in northern Wisconsin, always seems to taste a lot better than our tap water. A little bit more iron in it, but otherwise a much 'crisper' and 'fresher' taste than our tap water. It's very drinkable, straight from the tap. I would imagine that if they had the same filter system, they wouldn't notice as much of a difference as we did.
So can I prove that the filters are actually removing anything? No, not really. Other than $60/year worth of filters from my wallet. But I will say that if our current system broke, I would not hesitate to buy another.