How to clean hard soap scum and lime from bathtub?
I live on well water and have hard water stains (pink), and sometimes green from my pipes.  We use a product called CLR.  It stands for Calcium, lime, rust.  It works great on hard water spots and other deposits left by water.  You can buy it at Wal-Mart, Home Depot and probably your local grocery store.

The good thing about it is that you can just pour it on and let it sit for a bit.(read the bottle).  Then take a scrub brush and finish off the deposits.