The PURA UV Addon-1 is a one gallon/minute system is each designed as a single UV unit or can be used with an existing drinking water system. Compact, easily installed system, the Pura UV Addon-1 is a trouble free and easy to service system. They have no filters to change and require only an annual lamp change. The Add-On units are fitted with John Guest type 3/8 inch push-in quick connect fittings. Push in your 3/8 inch plastic or polypropylene tubing into the fitting for a tight, leak-free seal.