I purchased a cheap tds meter. When I get a chance I'll check my tap vs the brita filtered water. I did check it and the results were about the same. I did remember to let the water warm up a bit out of the fridge because apparently that effects the reading. I should really test the tank water as well.Ok BexM there is quite a smoke cloud around these type of filters. If it leaches k+ and H+ ions then it should be allright but your conductivity I believe will be a bit higher once passed through the brita which isnt bad sinceyoure adding k+ (if this is the case). Remember the only thing that takes things out of the water in the brita is the activated carbon. The cation exchange resin does as its name suggests just an exchange. It might take in some Ca++ but it puts out 2× Na+ or 2× k+.