A soakage pit (also called a soakhole or soakage system) is designed to disperse stormwater or greywater into the surrounding soil. When it fails, water has nowhere to go — and the signs are usually hard to miss. Here's how to tell if your soakage pit has given up the ghost and what to do about it.
What Is a Soakage Pit and How Does It Work?
A soakage pit is typically a rubble-filled or precast concrete chamber buried in the ground, connected to your downpipes or drainage system. It works by allowing water to slowly percolate outward into the surrounding soil. Over time, the soil's ability to absorb water can diminish, or the pit itself can become blocked or structurally compromised.
In New Zealand, soakage systems for stormwater must comply with NZ Building Code clause E1 (Surface Water), and their design depends heavily on local soil conditions and rainfall intensity. Always check with your local council before replacing or modifying a soakage system, as a building consent may be required depending on the scope of work.
Key Signs Your Soakage Pit Has Failed
1. Persistent Waterlogging or Ponding
If you notice standing water on your lawn or garden near the soakage pit — especially after moderate rainfall that wouldn't normally cause flooding — this is one of the clearest signs the pit is no longer draining effectively.
2. Soggy Ground That Doesn't Dry Out
A failed soakage pit often causes the surrounding soil to become permanently saturated. If a patch of your yard stays wet for days after rain, or feels spongy underfoot, the pit may be overwhelmed or blocked.
3. Water Backing Up in Downpipes or Gullies
If stormwater is overflowing from downpipe connections, backing up through gullies, or spilling out at ground level near the pit, the system is not coping. This can also indicate a blockage in the inlet pipe rather than the pit itself, so it's worth investigating both.
4. Subsidence or Collapse Around the Pit
A sunken or depressed area of ground above or near the pit can indicate the structure has collapsed inward. This is a safety hazard as well as a drainage problem — keep children and pets away from the area.
5. Foul Odours
If your soakage pit is connected to a greywater system (in some older properties), a failed pit can cause odours to surface. Note that connecting anything other than stormwater to a soakage pit may not comply with current regulations — check with your council.
6. Visible Overflow or Surface Discharge
Water visibly seeping or running across the surface from the pit area, particularly toward boundaries, driveways, or neighbouring properties, is a strong indicator of failure.
Common Causes of Soakage Pit Failure
| Cause | Explanation |
|---|---|
| Soil saturation | Clay-heavy or naturally wet soils lose permeability over time |
| Silt and sediment build-up | Fine particles clog the rubble fill and surrounding soil |
| Root intrusion | Tree roots can block inlet pipes or break pit walls |
| Structural collapse | Older pits made from loose rubble or timber can cave in |
| Undersized pit | Original pit may not have been designed for current roof area or rainfall |
| High water table | Seasonal rises in groundwater can overwhelm the system |
Can You Inspect It Yourself?
Homeowners can carry out a basic visual inspection — checking for ponding, soggy ground, and overflow at downpipe connections. If your pit has an access lid, you may be able to look inside to check the water level (a pit that is full and not dropping between rain events has likely failed).
However, do not enter or lean into a soakage pit. Confined spaces can contain low oxygen levels or toxic gases, and collapse is a real risk. For any hands-on investigation beyond a surface check, contact a professional.
For guidance on safe practices around excavation and confined spaces, refer to WorkSafe NZ.
What Happens Next — Repair or Replace?
Sometimes a soakage pit can be jetted or cleaned to restore partial function if the blockage is in the inlet pipe or the upper layer of fill. However, if the surrounding soil has become permanently saturated or the pit has collapsed, full replacement is usually necessary.
Replacement options include:
- A new, correctly sized soakage pit or soakhole
- A soakage trench system (often more effective in clay soils)
- Connection to the council stormwater network (where available and permitted)
The right solution depends on your soil type, site conditions, and local council rules. BRANZ provides technical guidance on stormwater management and soakage design that your drainlayer may reference.
When to Call a Professional
Drainlaying is restricted work in New Zealand. Under the Plumbers, Gasfitters, and Drainlayers Act 2006, any work that involves installing, replacing, or altering a drainage system — including soakage pits — must be carried out by, or under the supervision of, a licensed drainlayer. This is not optional; unlicensed drainage work is illegal and can affect your insurance and LIM report.
You can verify a drainlayer's licence through the Plumbers Gasfitters & Drainlayers Board.
Also check with MBIE Building Performance and your local council about whether a building consent is required for your replacement work — requirements vary by region and scope.
If you need a qualified local drainlayer, you can search for one on tradedirectory.co.nz.
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