USA Filtration Systems Duplex Filter System will replace the faucet-mounted water filter, counter-top system as well as the pitcher filtration system. Get Safe and Great Tasting Drinking Water Remove Lead, Chlorine, Cyst, PFAS and more from your drinking water. Our system can be installed under the sink to the existing plumbing or can be hooked up to your refrigerator. All parts are included, and the system can be easily installed in about 25 minutes. No need to call the plumber. The Duplex System is design for where dirty water or near a main road construction site.