Martina
I am using a Berkey Water Purifier (it's more than a water filter) as well and can highly recommend it! Its a countertop filter (chrome cylinders) that comes in a number of sizes. It comes with black filters and optional fluoride + arsenic filters. This is the only water we drink and I am extremely happy with it. It removes viruses to purification standards, pathogenic bacteria, cysts and parasites to non detectable levels, and harmful or unwanted chemicals to below detectable levels. Here is a link to their independent test results of the filtration: http://www.berkeyfilters.com/Test_results.pdf
They are not cheap, but the filters last 6,000 gallons. I have the smallest one (Travel Berkey) for just my Aussie and I, and I have to check a couple times/day the water level. The next size up would probably have been better for us, but I love it just the same.