In the early 80's I acquired a reverse osmotic filter. It was kind of pricey, but I traded a guy who sold them for one for some work on his house. It was a countertop model that had a hose that hooked up to a "dishwasher" adapter you installed on the faucet of the kitchen sink. As I recall, you set it (by adjusting the water flow) to 5 or so drips per 10 seconds (not sure at all about the numbers here). Every so often, you had to purge it by turning the water on full blast for a minute or two. Great tasting water, and no filter cost! Used it for about 8 years, no problems. Alas, it was damaged while I was overseas.
After that came a WaterPik filter that attached to the kitchen faucet again, but remained there. You could flip a lever to get unfiltered water for normal kitchen operations. This one had filters, but they lasted a reasonable amount of time. Brought this one back with me when I returned to The Hermit Kingdom, and did it match the fittings on the sink and continued to work very well. We were renting at the time and moved into a place that had the flexible hose type kitchen wand, so the WP went down the road.
For the last very many moons, a Brita countertop model has assumed the mantle. It's the large capacity, uses the classic filters, and works great, but it is a little cumbersome to move it to the place where you can fill it. The filters aren't too dear and last a reasonable length of time. Bad point, there are many square nooks and crannies that require regular cleaning which can get a bit tedious.
A note on the filters: the model I have has a device on the filler lid to tell you when to change the filter. Interestingly, it does not measure the flow of water, but rather relies on a timer. My wife and I are a two person household, but the time goes by regardless of the amount of water filtered. Lacking a chemistry set, mine gets changed when I notice a difference in the taste of the water.