Although reverse-osmosis plants can offer energy saving,the earliest membranes made from either polyamide fibers or cellulose acetate sheet, were fragile and had short life span, often no longer than three years These materials are highly susceptible to contaminants in
the source water-particularly chlorine, which harden the membranes, and microbes, which clog them.Pretreatment regimes, such as filtering out sediments and bacteria, must be extremely vigorous. A new generation of so-called thin composite membranes, made from polyamide films, promises to contamination, these new membranes are sturdier, provide better filtration and may last up to ten years.