Do you need a soakwell in Perth?
If your roof or paving sheds water, yes. The City of Wanneroo puts it plainly: "Property owners have a statutory obligation under common law precedents and the Local Government Act 1995 to confine water runoff within their property boundaries." The City of Joondalup's residential soakwells page uses the same wording, and the City of Cockburn cites section 3.25(1) of the Local Government Act 1995 for the same duty. The City of Stirling requires all rainfall falling within lot boundaries to be contained on site, by soakwells or approved alternatives such as holding tanks or infiltration basins.
Behind the council rules sits a state criterion. DWER's Decision process for stormwater management in Western Australia (2017) says runoff from the first 15 mm of rainfall should be managed at source, which for a house means on the lot. Soakwells are the usual answer on Perth sand, but not the only one: Wanneroo and the City of Rockingham both name spoon drains as an alternative. How a soakwell works, and how we install one, is on our soakwells in Perth hub.
Soakwell rules by council: the comparison table
Only verified rules appear below. Where a council's document is silent, the cell says so rather than guessing. Four of these councils have their own page on this site, linked in the first column.
| Council | Sizing rule | Setback from buildings and boundaries | Under driveways and paving | Design storm or basis | Source |
|---|---|---|---|---|---|
| City of Wanneroo | Table: 600 x 600 = 180 L serves about 14 m²; 900 x 600 = 385 L, 31 m²; 900 x 900 = 580 L, 47 m²; 1200 x 1200 = 1300 L, 111 m²; 1800 x 600 = 1550 L, 125 m²; 1800 x 1200 = 3100 L, 250 m². One downpipe per about 15 m² of roof, no more than 12 m apart | Minimum of the soakwell width, provided width is greater than or equal to depth; not recommended where clearances are narrow | Not stated in the homeowner sheet | Table "based on normal rainfall conditions" | Stormwater Runoff Information Sheet, July 2019 |
| City of Joondalup | Same six size table and same downpipe rule as Wanneroo | Same width rule as Wanneroo; overflow must not pond against the building or enter adjacent properties | Not stated | Not stated (no litres per m² rule published) | Residential soakwells (stormwater runoff) web page |
| City of Swan | Volume (m³) = 0.0122 x impervious area (m²), a general guide for sandy soil of high permeability | No closer than 1.8 m to a footing or property boundary | Trafficable lids on all soakwells in paved or concrete areas, accessible for maintenance | 5 year 10 minute storm; subsoil drains where maximum groundwater is less than 1.2 m below lot level | Property Development Design Guidelines D12, August 2016; Handbook of Stormwater Drainage Design, April 2022 |
| City of Stirling | Impervious area (m²) x 0.015 m = capacity (m³); minimum unit 900 mm diameter x 600 mm deep; roof runoff stored separately from paved area runoff | At least 1 m edge to edge, or manufacturer's specification if greater, unless a structural engineer certifies otherwise | Must be designed to be trafficable with an approved base to prevent subsidence of well liners | 1 in 1 ARI 60 minute event (15 mm) minimum; 1 in 20 where a drainage management plan is triggered | On Site Stormwater Drainage Criteria, June 2024 |
| City of Bayswater | Combined volume (m³) = impervious area (m²) x 0.0125; example 240 m² needs 3 m³ | Not stated | Accessways need soakwells and trafficable drains to keep runoff within the accessway | Retaining 12.5 mm of rainfall | Clearance of Subdivision Conditions Information Sheet |
| City of Canning (Canning Vale) | Drainage coefficient 0.0150 x impervious area; whole lot area used where the lot is under 300 m² | Not stated | Not stated | 1 in 20 year ARI with an overland flow path; 1 in 100 without one | Information Sheet, Stormwater Drainage, October 2020 |
| City of Cockburn | V = A divided by 80 (A = impervious m², V = m³); 1200 x 1200 serves 108.56 m² | Not stated | Not stated | 1 in 20 year storm of 5 minutes duration | On Site Drainage Requirements (Residential Lots), November 2019 |
| City of Gosnells | City's stormwater design calculator; 0.5 m clearance from soakwell base to maximum groundwater or clay; sealed tanks in poorly draining clay | At least the soakwell depth from footings and boundaries | Concrete soakwells preferred and required under all paved areas | 1 in 20 year ARI one hour with overland flow; 1 in 100 without | Stormwater drainage page and calculator guide, 2026 |
Sources: City of Wanneroo, Stormwater Runoff Information Sheet (July 2019); City of Joondalup, Residential soakwells (stormwater runoff); City of Swan, Specification D12 (August 2016) and Handbook of Stormwater Drainage Design (April 2022); City of Stirling, On Site Stormwater Drainage Criteria (June 2024); City of Bayswater, Clearance of Subdivision Conditions Information Sheet (2022); City of Canning, Information Sheet, Stormwater Drainage (October 2020); City of Cockburn, On Site Drainage Requirements (Residential Lots) (November 2019); City of Gosnells, Stormwater drainage and How to Use the Stormwater Design Calculator (2026). All checked 9 October 2026; councils revise these documents, so confirm the current version before you build.
What the rules have in common
Three ideas run through all eight documents. First, impervious area means everything that sheds water, not just the roof. Bayswater's wording is roofs, paving, driveways and patios, and the Town of Victoria Park goes as far as classing permeable type pavers as impervious for stormwater calculations. Second, setbacks exist so soaking water does not undermine footings, retaining walls or the neighbour's ground. Wanneroo's note that soakwells are not recommended where clearances are narrow, because there is not enough soil for the water to drain into, says why. Third, overflow must go away from the house and never onto a neighbour, the verge or the road. Joondalup requires overflow to be kept from ponding against the building or entering adjacent properties, and Swan states that "No stormwater is to be discharged from the property over the crossover or verge onto the roadway or any right of carriageway."
One caution on the Swan figures: they come from engineering guidelines written for development sites rather than single houses, so confirm the rule for your lot with the City. For the arithmetic behind each formula, with 150, 250 and 400 m² lots worked through, see our soakwell cost and sizing page with worked sizing examples.
Permits and approvals: check with your council
The Building Regulations 2012 do not list soakwells or paving in the Schedule 4 exemptions, and they do not say that a permit is or is not needed for them. Whether a soakwell counts as building work is decided by the permit authority, which is your local government. The Wanneroo, Joondalup, Swan and Stirling soakwell documents do not mention a building permit at all. So this page does not claim a permit is required and does not claim one is not: check with your council about approvals for your site.
Where soakwells form part of a building or development application, they appear on the drainage plan. Stirling requires stormwater disposal details to go to its Development Services Business Unit at the development approval stage, and Canning and Gosnells both require a stormwater drainage plan to be approved for all developments. For a homeowner question, Wanneroo Building Services is on 9405 5000 and Joondalup Building Services on 9400 4000.
Clay, limestone and high water table sites
The standard rules assume Perth sand. Where the ground is different, the documents change tack. Gosnells requires sealed tanks in poorly draining clay and 0.5 m between the soakwell base and maximum groundwater. Swan requires subsoil drains where the maximum groundwater level is less than 1.2 m below lot level. Stirling triggers a drainage management plan where groundwater is within 1.2 m of the surface and allows holding tanks and infiltration basins as approved alternatives. Nedlands advises shallow, larger diameter units where the water table is high. DWER's Perth groundwater map estimates the depth to the water table beneath any property.
In the northern suburbs the pattern is simple to state. Bassendean sand across the northern corridor drains fast. Spearwood sand over limestone on the coastal side drains fast too but can hit caprock on excavation. Guildford Formation clay around Dayton and Midland drains poorly. More in our guide to soakwells in clay, limestone and high water table areas.
How IBP applies the rule on your job
We are based in Landsdale, so the City of Wanneroo is our home council, but we work to the rule for whichever council your lot sits in. On site we measure the roof and paved area, count the downpipes, set each unit back to that council's figure, use trafficable units under driveways and reinstate the paving when the pit is closed. Over 20 years of experience and a lifetime workmanship warranty stand behind the work.
Council pages in detail
City of Wanneroo soakwell requirements: the six size capacity table, the one downpipe per 15 m² rule and the width based setback, worked for a 240 m² Landsdale lot.
City of Joondalup soakwell requirements: the same table as Wanneroo, with no litres per square metre rule published, plus the limestone and lake side ground in Joondalup suburbs.
City of Stirling soakwell requirements: the 15 mm formula, the 1 m setback, the 900 x 600 minimum and separate storage for roof and paving water.
City of Swan soakwell requirements: the 0.0122 formula, the 1.8 m setback and trafficable lids in paved areas, with the sand to clay split across the City. For the suburbs we cover in each council, see areas we service.
