How Bilby works
Drainage and water-management costs
Three kinds of water work
Dewatering keeps an excavation workable during construction. Foundation drainage manages water around the building. Local stormwater measures collect, infiltrate or store runoff on the plot. They have different quantities and ownership; a municipal stormwater tariff is a separate connection charge.
Read what the selected package includes
Native groundwork can price dewatering when groundwater evidence warrants it, but does not separately price every perimeter-drainage design. The reference normal-groundwork package contains a drainage component. Basement reference scope can already include drainage. Local infiltration/storage excludes perimeter drainage already counted and engineered flood protection. Special driveway drainage also has separate scope.
Evidence and dimensions
Mapped groundwater risk and soil type do not prove an infiltration system will work. A designed outlet and local requirements need confirmation.
| Input | Unit | Where from? |
|---|---|---|
| Groundwater evidence | condition | Ground assessment |
| Foundation perimeter | m | Geometry or disclosed reference assumption |
| Water-management design | system | Project specification or broad allowance |
| Included drainage | scope | Basement/groundwork/supplier package |
Native allowance and reference costs
Native dewatering is selected from a severity allowance only when evidence is present; a possible-groundwater warning alone is not automatically a pump bill. The standalone dewatering reference is SEK 5,000 / 15,000 / 50,000. Reference perimeter drainage is metres × SEK 350 / 600 / 1,000. An ordinary small local stormwater system is a fixed SEK 15,000 / 35,000 / 80,000. Project-specific amounts precede these references, and owned components add zero to an already counted parent.
Illustrative perimeter drainage
A fictional 50 m foundation perimeter gives SEK 17,500 / 30,000 / 50,000 in the drainage reference. If an ordinary separate stormwater system is also needed, those two independent scopes sum to 32,500 / 65,000 / 130,000. If drainage is included in the basement package, only the stormwater allowance is additional. Municipal tariffs are not part of this example.
Water needs a real outlet
Elevation, soil permeability, groundwater, roof runoff, storage volume and discharge arrangements influence a real design and price. The fixed allowance does not calculate a rain-event capacity or grant discharge permission. Missing data is not proof of dry ground. Compare the receipt and supplier inclusions before entering a manual price.
Method and evidence
Reviewed 18 October 2026, native groundwater-conditioned scope and 2026 reference catalogue researched 16 September. Geological water layers are context rather than a drainage design or price source SGU. Confirm site drainage with the designer and municipal charges with the relevant VA tariff.
The review date covers this explanation and its implemented method. Price and data dates are stated separately in the article.