I have installed about 8 of these kinds of system and to tell the truth I am really disappointed int the Whirlpool variety. The first round of filters had 48 PPM which is OK, but in a short span of time it wore out and the only two people in my house are my wife and I. The next filters pack never got better than 141 PPM, the next pack never got better than 177, the next pack never got better than 238 PPM.... I am done. I followed directions carefully and yet it made no difference. I bought the whirlpool brand filters This system just doesn't work.