Hydrotech 41400076 Dual Purpose Water Filter fits Hydrotech HT and HTF Series Reverse Osmosis Systems. It is a dual purpose water filter that provides both carbon and sediment filtration in one filter. The Hydrotech 41400076 water filter should be replaced every 6-12 months depending on your water quality and water usage. The Hydrotech 41400076 water filter is often used in the first stage on Hydrotech 3 Vessel RO systems with CTA membranes.