Test first, then buy only what the test calls for. Most wells need one or two systems. Sand takes a sediment filter; rust or black stains and a rotten egg smell take an iron filter; hard water takes a softener; blue-green stains take an acid neutralizer; bacteria takes a UV light. Of 344 well tests my customers sent in, more than half showed one of those problems or none. Here is the match, with today's price for each system.