A broad category encompassing the many ways we bring water in, consume it or use it for heating, cooking, and cleaning, and then dispose of it in the form of waste water. Subcategories include water heaters (traditional models as well as “instant” heaters that don’t require tanks), water filtration systems, heat exchangers that transfer energy from wastewater to freshwater, and eco-friendly use strategies like graywater systems and rainwater catchment and storage.