Around 66 % of all building damage in Switzerland is water damage (HEV) — yet building-water insurance (Gebäudewasser-Versicherung) is not mandatory in any canton. It closes the gap that cantonal building insurers (KGV) deliberately leave open: pipe burst, seepage water, oil-tank leak. Typical annual premium 0.3–0.5 ‰ of the building value, deductible (Selbstbehalt) CHF 200–500. With damage of CHF 8'000 to 150'000 per event, taking out the voluntary policy almost always pays off.
Covered are sudden water risks from inside and outside: pipe and water-line bursts, water escaping from a washing machine or boiler, backflow from the sewer, seepage water through the roof or wall after heavy rain, frost damage, as well as heating-oil and brine leakage (often as a module). Search and break-open costs for locating the leak are co-insured up to CHF 10'000 — for rented properties, additionally loss of rent up to 24 months.
The cantonal building insurance covers fire and natural hazards (storm, hail, flooding, avalanches) on a mandatory basis. Pipe water, backflow and seepage water, by contrast, are not necessarily insured. In the canton of Zurich, the GVZ explicitly covers no water damage from a pipe burst, backflow, groundwater or leaky roof/floor constructions — anyone who buys without an add-on bears these, around two thirds of all building damage, entirely themselves. In ZH, BS, ZG, GE, TI, VS and others, a separate private policy is needed; in cantons such as AG, BE (module), LU or SG the water cover can be co-insured directly as a KGV module.
A small pipe burst in the wall typically costs CHF 8'000 (search costs CHF 1'500–3'000, drying CHF 2'000–4'000, floor covering CHF 3'000–6'000). Seepage damage through a flat roof adds up, including drying and mould, to around CHF 25'000 (range CHF 15'000–40'000). An oil-tank leak comes in at CHF 60'000+ for soil remediation and disposal — peak values above CHF 150'000. A heating defect with water leakage works out to about CHF 4'500.
Excluded in all common Swiss policies are: flooding and inundation (natural-hazard loss), groundwater without a flooding event, inadequate maintenance, construction and design defects, pre-existing damage at the time of taking out the policy, gradual saturation and earthquakes. The most frequent reason for rejection is «inadequate maintenance»: the heating-oil tank must be inspected every 10 years (a cantonal obligation). Pre-existing damage must be reported — concealment risks retroactive rescission for breach of the duty of disclosure (Art. 4 et seq. VVG).
The deductible is usually CHF 200–500, selectable up to CHF 2'500. Raising it to CHF 500 lowers the premium, depending on the provider, by 8 % to 18 %. For the sum insured (building insured value, not purchase price) it pays to check the sublimits: search costs at least CHF 10'000, heating-oil damage CHF 50'000–200'000, mould remediation CHF 10'000–25'000, loss of rent 12–24 months.
With annual premiums of CHF 350–500 (or CHF 280–320 via a cantonal water module such as AGV Aargau, model house CHF 1'000'000 insured value) and damage of CHF 8'000 to 150'000, the expected value is almost always positive. The policy is practically indispensable with a heating-oil tank (median CHF 30'000–60'000 remediation, hazard liability under ZGB), for buildings over 30 years old, in the cantons ZH, BS, ZG, GE, TI, VS and for rented properties.