Kattoveden

Kattoveden, literally “roof water” in Finnish, denotes rainwater that runs off roof surfaces and is captured for later use. It is a central element of rainwater harvesting, often employed to supplement municipal water for non-potable applications such as garden irrigation, car washing, toilet flushing, and outdoor cleaning.

A typical kattoveden system includes the roof surface, gutters and downspouts, a first-flush diverter to discard the initial, debris-laden runoff, a storage container such as a tank or cistern, and, in many setups, filtration and disinfection stages. The water quality is influenced by roof material, coatings, and environmental factors; debris, bird droppings, and atmospheric pollutants can contaminate the supply. For non-potable uses, filtration and, if necessary, disinfection are commonly recommended. Drinking rainwater requires higher treatment standards and is subject to stricter regulations.

Advantages of kattoveden include reduced municipal water demand, lower stormwater runoff, and potential cost savings, especially in regions with dry summers or high rainfall variability. Limitations include seasonal availability, potential for freezing in cold climates, and the maintenance burden of cleaning gutters, screens, and tanks.

Regulatory aspects vary by country and region. In Finland, rainwater harvesting is generally permissible, but using it for drinking or food preparation typically requires rigorous treatment and compliance with local health and safety regulations. Kattoveden systems are widely used in sustainable building and rural settings as a complement to conventional water supplies.