Current federal standards do not regulate water use or performance of water softeners. However, there is an industry standard for water softeners, NSF/ANSI 44-2004 Residential Cation Exchange Water Softeners, which many states have adopted as part of their plumbing codes.
You may need a PDF reader to view some of the files on this page. See EPA’s About PDF page to learn more.- WS-products-noi-water-softners.pdf (PDF)(8 pp, 56 K)