content: When I got the product and opened the box, the literature said that you cannot use the kind of shower head that has a valve that turns off the flow. This is because the filter housing is plastic and is subject to cracking or bursting if you turn off the flow downstream from the filter.That's the kind of shower head I have, and I like to use the valve feature. I really really wish that eGeneralMedical had said this in their (limited) online literature. And they expect me to pay the return shipping and a 15% restocking fee!