Your obligation in the City of Wanneroo
The City's Stormwater Runoff Information Sheet opens with the rule every other rule hangs off: "Property owners have a statutory obligation under common law precedents and the Local Government Act 1995 to confine water runoff within their property boundaries." It then names the method: "The most effective way to achieve this objective is to provide catchment areas such as soakwells, spoon drains or similar methods to disperse the rainwater collected from gutters and downpipes from roof and paved areas."
The same expectation sits in the City's planning framework. Local Planning Policy 4.4 Urban Water Management, adopted 5 May 2020, carries the model condition "All stormwater runoff shall be retained onsite". So whether the question comes up at the building stage or later when you add a patio or a driveway, the answer in Wanneroo is the same: the water stays on your lot. To see how that compares with the councils next door, read our page on how Wanneroo compares with other Perth councils.
The City's soakwell capacity table
Wanneroo does not publish a litres per square metre formula for homeowners. It publishes a table of what it calls common sizes of concrete soakwells, with the approximate surface area each one drains.
| Internal diameter (mm) | Length (mm) | Capacity (L) | Approximate surface area drained (m²) |
|---|---|---|---|
| 600 | 600 | 180 | 14 |
| 900 | 600 | 385 | 31 |
| 900 | 900 | 580 | 47 |
| 1200 | 1200 | 1300 | 111 |
| 1800 | 600 | 1550 | 125 |
| 1800 | 1200 | 3100 | 250 |
"The calculations provided above are recommended based on normal rainfall conditions. Excessive stormwater conditions can cause overflow depending on the soil type, eg: clay, limestone, etc."
Source: City of Wanneroo, Stormwater Runoff Information Sheet (correct as of July 2019).
To use the table, add up the roof and every paved area that drains to the system, then pick units whose areas drained add up to at least that figure. Where several options fit, the setback rule below usually decides. The same table is worked for 150, 250 and 400 m² on our soakwell cost and sizing page.
Downpipes: one per 15 m², no more than 12 m apart
The sheet is specific: "One downpipe is required for approximately 15 square metres of roof area. The distance between downpipes should not exceed 12metres in accordance with the Building Code of Australia." The downpipe rule sizes the collection; the table sizes the storage. They are separate sums, and one does not mean a soakwell under every downpipe. Downpipes are piped underground to shared units, so a roof with twelve downpipes can drain to two or three soakwells placed where the setback rule allows.
Setbacks from buildings and boundaries
"As a general guide the setbacks for soakwells should be a minimum of the width of the soakwell away from buildings and boundaries, providing that the width is greater or equal to the depth of the soakwell." The City adds a warning that matters on modern lots: "It is not recommended to install soakwells where there are narrow clearances between buildings and boundaries as there would not be sufficient drainage area for water to be drained into the soil."
In practice, on the 2000s estates in Landsdale, Darch and Banksia Grove, the side setback is the limiting factor. A 1.2 m wide unit cannot sit in a 1.0 m side passage and still meet the rule, and Banksia Grove's newer precincts were laid out on narrow lots. The units go to the front or rear yard, and the downpipes along the side of the house are piped to them.
Worked example: a 240 m² lot in Landsdale
Take a two storey home in Landsdale with a 180 m² roof plus 60 m² of driveway and alfresco paving draining to the same system, so 240 m² of impervious area.
- Storage from the table. One 1800 x 1200 unit serves about 250 m² (3100 L), or three 1200 x 1200 units serve about 333 m² (3900 L). Both cover 240 m². Unit counts are estimates and we confirm them on site.
- Downpipes. 180 m² divided by 15 gives 12 downpipes, piped in groups to the units.
- Setback. A 1200 x 1200 unit is 1.2 m wide and 1.2 m deep, so width equals depth and the setback is 1.2 m from walls and boundaries. An 1800 x 1200 unit is 1.8 m wide and 1.2 m deep, so its setback is 1.8 m, which rules it out of any side setback and pushes it to a rear yard with room to spare.
- Soil. Landsdale sits on Bassendean sand, inferred from adjoining Wangara, which the City lists as Bassendean. It is deep, pale grey and free draining, so deep units suit it.
The caveat is the City's own: the table assumes normal rainfall and sandy soil. In low ground near the constructed lakes in Landsdale Gardens we keep the soakwell base above the water table, which can mean more, shallower units.
What the City also publishes for designers
Alongside the homeowner sheet, the City's Development Design Specification WD5 Stormwater Drainage Design (June 2019) says "Soakwell sizing may be based on 1cum per 60sqm of constructed impervious surface runoff area" and requires infiltration systems to sit at least 0.3 m above the maximum groundwater level. WD5 is written for designers and subdivision work rather than homeowners, so for a house the information sheet is the document to use, and the City's Building Services on 9405 5000 can confirm which applies to your job. The City does not state a 1 in 10 or 1 in 20 year storm rule for single houses, so we do not claim one.
What the sheet does not say: check with the City
Several things people ask about are simply not stated in the City's sheet, and we do not fill the gap with guesses. The sheet does not say whether a building permit is needed for soakwells on their own. It does not give a trafficable lid or under driveway rule. It gives no litres per square metre formula for homeowners and no high water table rule for single houses. On each of these, check with the City of Wanneroo Building Services on 9405 5000 about approvals for your site.
Soakwells in City of Wanneroo suburbs
IBP Paving is based in Landsdale, inside the City, so Wanneroo's rule is the one we work to most often. We install and replace soakwells in Landsdale, Darch, Madeley, Wanneroo, Banksia Grove and Tapping, usually as part of a driveway, alfresco or pool paving job. Over 20 years of experience and a lifetime workmanship warranty on every job. For the full list of suburbs, see areas we service.
Sources: City of Wanneroo, "Information Sheet, Stormwater Runoff" (correct as of July 2019), wanneroo.wa.gov.au stormwater runoff information sheet; City of Wanneroo, "Development Design Specification WD5 Stormwater Drainage Design" (June 2019), wanneroo.wa.gov.au WD5; City of Wanneroo, "Local Planning Policy 4.4: Urban Water Management" (adopted 5 May 2020). Accessed 9 October 2026; the City revises these documents, so confirm the current version before you build.
