Rainwater Harvesting. Renergise The Leading Supplier of Rainwater Systems And Supper Slim Rainwater Wall Tanks. Rainwater harvesting is a technique used for collecting, storing, and using rainwater for landscape irrigation and other uses. The rainwater is collected from various hard surfaces such as roof tops and/or other types of manmade above ground hard surfaces. Renergise supply Rainwater tanks and rainwater systems for the storage of water for your home and garden use. The collected rain water can be used for any process once it is non consumption and non-bathing. We supply rainwater systems for applications across these sectors domestic, commercial, agriculture, public. Renergise Slim Rainwater Wall Tanks are a slim rainwater wall tank and systems that can easily be installed above ground in a confined space.