Watts TFC-100 gpd Membrane This membrane is rated at 100 Gallons Per Day.  Actual production in your R.O. system will vary, and normally produces around half of the advertised rating.   If you have chlorinated water, we recommend you use a Carbon / Sediment Pre Filter.  The residual chlorine in " city " water will destroy the Thin Film Composite ( TFC ) membrane.  Fits most standard RO units including but not limited to the Flowmatic FMRO4J, FMRO4G, FMRO5G, FMRO5GP, and model 5SV.The W1812100 membrane is 1.8" x 11.8"Membrane should be changed every 2-5 years depending on water quality and usage.Watts