Water Management on Construction Sites
Drainage and stormwater management is fundamental to any construction project in New Zealand. Get it wrong — whether through inadequate design, poor installation, or failure to manage stormwater during construction — and you face a range of problems: building consent non-compliance, flooding and water damage during construction, complaints from neighbours and downstream landowners, and resource consent issues with the regional council.
Understanding the drainage requirements for residential and commercial construction, and how to install drainage systems correctly, is essential knowledge for builders and civil contractors working in the New Zealand market.
The Two Drainage Systems
New Zealand’s building and infrastructure standards distinguish between two drainage systems that must be kept separate: the wastewater system (carrying sewage and greywater from plumbing fixtures to the reticulated sewer or septic tank) and the stormwater system (carrying rainwater from roofs, paved areas, and the site to the stormwater infrastructure or waterway). Mixing these systems — a common cause of pollution in older New Zealand towns — is prohibited under resource and building consents.
On residential sites, the wastewater drainage requires a licenced drainlayer to carry out the work. Stormwater drainage — connections from downpipes, surface drains, and site drainage to the stormwater system — is also typically drainlayer work for connections to public infrastructure, and requires compliance with the local authority’s stormwater management requirements.
Site Erosion and Sediment Control
Construction sites are major sources of sediment pollution, and regional councils require sediment and erosion control plans for construction activities above certain scales. Silt fences, sediment traps, and tracking pads at site exits are standard erosion control measures. During high-rainfall events, construction sites without adequate controls can discharge large quantities of sediment to stormwater systems and waterways, causing ecological damage and triggering resource consent enforcement action.