Since debuting in US stores in mid-April, Cirkul has sold 1.5 million units and is one of the top-performing items in the home department, the world’s largest retailer told shareholders this month.

Cirkul is sold in home sections because it’s an appliance of sorts. Users fill the Cirkul-branded plastic bottle with water, insert a flavor cartridge and set an intensity dial to customize options ranging from iced coffee to strawberry lime. Starter kits with a bottle and two cartridges sell for about $20.