Pump Stations for Low Lying and Flood Prone Blocks
Written for Australian homeowners, builders and plumbers dealing with a block that sits lower than everything around it.
Sizing a stormwater pit? Our stormwater pump sizing calculator works out the peak runoff for your area and postcode, the pit size and the pump you need.
Low lying block drainage is the problem of getting water and waste to travel uphill, and the only reliable fix is a pump station: a sealed tank that collects the flow and lifts it to the sewer or stormwater main. Gravity drainage will not work on a site where the outlet sits above the inlet. No amount of extra pipe fall, agi drain or regrading changes that. You either pump, or the water stays.
That is the whole answer. What follows is how to do it without buying the wrong unit.
What makes a block low lying in drainage terms
A block is low lying when any fixture or drainage point sits below the invert level of the council main it has to discharge into. Invert level means the inside bottom of the main, and it is the number on the sewer diagram or the stormwater plan that decides everything.
Plenty of blocks look flat and still fail this test. A house on a gentle slope with a basement laundry is a low lying drainage site even though the front yard drains fine. Equally, a block can sit visibly in a dip and still have a deep enough main to drain by gravity. Do not eyeball it. Get the levels.
Flood prone is a separate problem
Flood prone means the site takes water from somewhere else during heavy rain, which is a volume problem rather than a level problem. A low lying block has nowhere to send its own water. A flood prone block has other people's water arriving on top of that. Many sites are both, and those two problems want different answers.
Low lying alone: size the pump for the fixtures and the lift. Flood prone as well: size for the peak storm inflow, add storage, and take backflow seriously.
Stormwater or sewer, and why it matters more here
You need a stormwater pump station for rainwater, roof runoff, driveway water and basement seepage, and a sewer pump station for anything that leaves a toilet, kitchen or laundry. On a low lying block you often need both, as two separate systems, because mixing them is not allowed and the pumps are built for different jobs.
The tanks look near enough to identical. The machine inside is not. A stormwater station runs a drainage or vortex pump built for high flow with no cutter. A sewer station runs a grinder or cutter pump built to chew solids at lower flow. Feed sewage into a drainage pump and it blocks, usually on a wet wipe, usually at the worst time.
If this is new to you, the detail sits in our guide to grinder pumps versus drainage pumps.
Sizing a stormwater pump station for a flood prone site
Size a flood prone stormwater station on peak inflow, not on tank litres. Peak inflow is roughly the catchment area draining to the pit multiplied by the rainfall intensity your hydraulic consultant or plumber works to for the area.
A rough field version: a 200 square metre roof and paved area in a 50mm per hour downpour produces about 10,000 litres in that hour, so roughly 170 litres a minute. A pump rated at 12,000 litres an hour at zero head will not deliver 12,000 at 6 metres of lift. Read the curve at your actual head, then add margin.
Storage buys you time, and time is the point
Tank volume on a flood prone block is buffer for a power cut or a pump that cannot keep up, so bigger is genuinely better here. On an ordinary low lying block a small pit is fine because the pump simply cycles more often. On a flood prone one, the twenty minutes of storage you bought is the twenty minutes between a working pump and water through the back door.
| Situation | Typical unit | Why | From (inc GST) |
|---|---|---|---|
| Small yard, driveway or lightwell | REEFE Stormwater Pit & Pump | 40L, 85L and 180L pits, preassembled, domestic runoff | $799 |
| Whole house roof and paving | Kwikflo 250L Stormwater Station | 250L tank, AL750 drainage pump, fits a standard doorway | $2,607 |
| Large site or genuine flood risk | Kwikflo 900L Stormwater Station | 900L of buffer before the water has anywhere else to go | $3,206 |
| Site that cannot afford a failure | Kwikflo Dual Stormwater Station | Two pumps, alternating, one keeps working if the other stops | $5,297 |
Prices are Waternex list prices in AUD including GST, current as of September 2026.
The full range sits in Stormwater Pit and Pump Systems. For pit and cover sizing specifically, read stormwater pit sizing for Australian homes.
Sizing the sewer station when the drain sits below the main
A 250L sewer pump station handles most low lying residential jobs: a granny flat, a basement bathroom, a laundry, a single amenities block. Step up to 900L for a whole house and 1200L for a large home or light commercial.
The figures behind that, retyped so they are readable without opening the drawing:
| Tank | Depth | Diameter | Suits |
|---|---|---|---|
| 250L | 880mm | 720mm | Granny flat, basement bathroom, low section of an existing house |
| 900L | 1200mm | 1075mm | Full house, 3 to 4 bedrooms |
| 1200L | 1600mm | 1075mm | Large home, light commercial, dual pump |
On a low lying block the depth column matters twice over. The tank has to sit below the fixtures it serves, so a deep tank on an already low site can put you into a very wet hole. Ask your excavator about the water table before you commit to the 1200L.
Shop the range in Sewer Pump Stations, or compare the three sizes in our 250L versus 900L versus 1200L breakdown.
Head height decides the pump, and low blocks have more of it
Head is the vertical lift plus friction loss in the pipe, and on a low lying block it is almost always higher than people expect. Add the pit depth, the climb to the highest point in the discharge line, and roughly one metre for every 10 metres of horizontal run.
Worked example. Pit 1.2m deep, the line climbs 2.5m to clear a retaining wall, 40m of pipe to the main. That is 3.7m static plus about 4m friction, so 7.7m of head. Buy a pump comfortably above that, never one rated at exactly the number.
Full method here: how to calculate head height for a pump station.
Backflow, power and the two failures that actually flood houses
The two things that flood a low lying property are a power cut during a storm and backflow from a surcharging main. Neither is a pump sizing problem, and neither is optional to plan for.
Backflow prevention
A sealed pump station with a non return valve on the discharge line is itself a backflow barrier, which is one of the underrated reasons to pump on a low block even where gravity just barely works. Water in a surcharging main cannot travel back down the rising main and out your lowest gully. Check the valve is there, and check it annually.
Power
A pump station does nothing without power, so on a genuinely flood prone site the pump circuit deserves its own thinking: a dedicated circuit, a high level alarm, and a generator inlet or battery backup if the site cannot tolerate a wet floor. A dual pump station protects against a failed pump. It does not protect against a failed grid.
Get an alarm either way. Ours are covered in what a pump station alarm actually means.
Access covers on a block that floods
Specify a load rated access cover if the pit sits anywhere a vehicle might cross, and a sealed cover if the pit sits where surface water pools. Pedestrian rated lids ship as standard on most packages, which is fine in a garden bed and wrong under a driveway.
A Class D trafficable cast iron cover costs a fraction of retrofitting one through finished concrete. The classes are explained in access cover classes A to G.
Four mistakes we see on low lying jobs
Treating stormwater and sewer as one problem. They need separate systems and different pumps. Plan for two.
Sizing the stormwater pump on the tank, not the storm. Peak inflow sets the pump. Tank volume only buys time.
Single pump on a site that floods. If a stopped pump means water inside, the second pump is cheaper than the carpet.
No thought about access. A 1075mm tank does not fit down a 900mm side path. Measure the route in before you order the hole.
Frequently asked questions
Do I need a pump station on a low lying block in Australia?
You need a pump station whenever a fixture or drainage point sits below the invert level of the main it discharges to, which is common on low lying blocks. Your plumber confirms it from the sewer diagram or stormwater plan, not from how the site looks.
What size stormwater pump station does a flood prone block need?
Size it on peak inflow to the pit, which is catchment area multiplied by rainfall intensity, then add storage as buffer. A typical house roof and paved area runs a 250L station, while a genuinely flood prone site is better on 900L or a dual pump setup.
Can a pump station stop my house flooding from the street?
A sealed pump station with a non return valve stops backflow coming up through your own drainage during a surcharge, and that is a real benefit on a low block. It does nothing about overland flow across the surface, which is a site grading and bunding question for your builder.
What happens to a pump station in a power cut?
The pump stops and the tank fills to whatever storage it has, which is why tank volume matters on flood prone sites. Options are a generator inlet on the pump circuit, a battery backed alarm so you know early, or simply a bigger tank.
Can one pump station handle both stormwater and sewage?
No, keep them separate. Stormwater and sewer are legally separate systems in Australia and the pumps are built for different duties, so a combined station is both a compliance problem and a reliability problem.
Send us the levels and we will tell you what fits
Give us the pit depth, the lift to the main, the pipe run and whether it is stormwater, sewer or both. We will tell you which unit suits and what it costs, before anyone digs.
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This guide is general information for Australian conditions and isn't a substitute for advice from a licensed plumber. Pump station installation, sewer connection and stormwater discharge are regulated work, and requirements differ between states and water authorities. Have your plumber confirm levels, sizing, approvals and compliance before you order.