Answer: -hope to insert a "T" device to divert some flow to the espresso machine Yeah. And the valve at C needs to be turned fully clockwise to stop the flow of water. Beneath the red handle you'll find a brass "packing nut." If the valve isn't too worn out, tightening this packing nut (clockwise) with a crescent wrench will stop or at least reduce to a minimum any leaks along the stem of the valve. You can use moderate force but don't go crazy on the poor thing. Also, tightening the packing nut will make the valve itself harder to open and close. -Firstly, you would need to install some sort of inline softener, unless your water supply is particularly soft, and this in addition to your other questions leads me to believe you should call a reasonably priced plumber.