Stormwater vs Sewer: Which Pump Station You Need and Why You Can't Mix Them
Stormwater vs sewer, for homeowners, builders and plumbers with one low spot, two kinds of water and a bright idea about sharing a tank. Don't.
Stormwater and sewer are two separate systems, and in Australia they must stay separate. Stormwater is rain off roofs and hard surfaces, and it goes to the council's drainage. Sewage is everything from toilets, showers, sinks and laundries, and it goes to the water authority's sewer. So if you need to pump both, you need two stations, not one bigger one.
The good news: picking the right one is easy. A sewer job wants a cutter or grinder pump, such as the Kwikflo 250L Sewer Pump Station at $3,199. A rain job wants a drainage pump, such as the REEFE Stormwater Pit and Pump from $799.
Short on time? See sewer pump stations, see stormwater pit and pump systems, or use the pump station sizing calculator to work out your tank, head and flow.
Stormwater vs sewer at a glance
The difference between stormwater and sewer comes down to what is in the water, where it goes and how fast it arrives.
| Stormwater | Sewer | |
|---|---|---|
| What it carries | Rain, silt, leaves, grit | Toilet waste, paper, greywater |
| Where it goes | Council drainage, kerb or legal point of discharge | Water authority sewer main |
| How it arrives | Huge bursts, then nothing for weeks | Small amounts, every day |
| Pump type | Drainage or vortex pump | Cutter or grinder pump |
| Sized on | Peak inflow in a storm | People in the building, plus reserve |
| Lid | Grate is common | Gastight |
| Entry price with us | From $799 | From $3,199 |
Prices current as of November 2026, AUD including GST.
Why you can't connect stormwater to sewer
You can't connect stormwater to sewer because rain would overload the sewer, and Australian water authorities generally prohibit it. Sewer mains are sized for what people flush, not for what a storm drops on a roof. Send roof water into them and the system surcharges, which means raw sewage comes up through overflow gullies and manholes, often in someone else's yard.
The size of the problem is easy to show. A 100 square metre roof in a storm dropping 100 mm an hour sheds about 167 litres a minute. A four person house averages less than a litre a minute across a whole day. One roof can out-flow a whole street of houses.
It fails the other way too. Sewage in a stormwater line ends up untreated in a creek or on the beach. Either direction is a cross connection, and authorities look for them. If you find one on an existing property, have your licensed plumber fix it before the water authority finds it for you.
Why one tank can't do both jobs
One tank can't do both jobs because a shared pit has one discharge, and a stormwater system and a sewer system must end up in different places. Even if the pump could handle it, the moment rain and sewage meet in a tank, the contents are sewage. All of it now has to go to sewer, and that is the connection you are not allowed to make.
There is a practical problem as well. A sewer station has a gastight lid so the smell and gas stay in. A stormwater pit often has a grate so the water can get in. Those two needs do not fit on one lid.
Sewer pumps and stormwater pumps are different machines
A sewer pump has to chop or pass solids, and a stormwater pump only has to move dirty water fast. That single difference sets the price gap.
Take the Kwikflo 250L. The sewer package at $3,199 and the stormwater package at $2,607.29 use the same KPPS250 tank. What changes is the pump inside it. The sewer version carries an ALC750 high head cutter pump, built to shred solids, with 14 metres of maximum head. The stormwater version carries an AL750-1A drainage pump with an open multi-vane vortex design, passing solids up to 20 mm at up to 380 L/min.
Put a drainage pump on raw sewage and rags and wipes will find it. Put a cutter pump on stormwater and it will work, but you have paid more for a blade that has nothing to cut, and grit is not kind to cutters. Our guide to grinder pumps vs drainage pumps goes further.
One warning on small stormwater pits. The REEFE Stormwater Pit and Pump is listed as not suitable for raw sewage. Believe the listing.
How each station gets sized
A sewer station is sized on people and a stormwater station is sized on storms, so the same block can need very different tanks. Get this backwards and you end up with a big sewer tank that does nothing, or a small stormwater pit that floods on the first wet night of summer.
Sewer sizing
Sewer sizing starts with the number of people or bathrooms, plus enough reserve to hold the waste when the power is out. A 250L tank suits a granny flat or small basement. A family house, or anything with a long run to the main, usually steps up to 900L. See 250L vs 900L vs 1200L for the detail.
Stormwater sizing
Stormwater sizing starts with catchment area and rainfall intensity. Area in square metres, times rainfall in mm an hour, divided by 60, gives litres a minute. A 200 square metre driveway and roof in a 100 mm an hour storm makes about 333 L/min. Your pump has to keep up with that at your actual head, or the pit has to store the difference.
The rainfall figure for your site comes from your plumber or hydraulic designer, not from us. Our guide to stormwater pit sizing walks through the numbers.
Which station should you buy?
The right station depends on the water and the volume, and the table below matches common jobs to live products.
| Job | Station | Pump | Price |
|---|---|---|---|
| Granny flat or basement bathroom | Kwikflo 250L Sewer | 0.75 kW cutter | From $3,199 |
| Same job, grinder pump and alarm | REEFE RGM055A 250L Sewer | 0.55 kW grinder | $3,305 |
| Whole house below the main | Kwikflo 900L Sewer | Cutter | $4,699 |
| Low courtyard or small paved area | REEFE Stormwater Pit and Pump | RVS155VF | $799 to $1,250 |
| Tight basement drainage | Kwikflo 250L Stormwater | 0.75 kW drainage | $2,607.29 |
| Larger catchment | Kwikflo 900L Stormwater | 0.75 kW drainage | $3,206.03 |
| Large catchment or high head | Kwikflo 900L Stormwater, 1.5 kW | 1.5 kW drainage | $4,038.62 |
Prices current as of November 2026, AUD including GST.
Need both on one site? Budget for both, and keep them apart. A low lying block with a house below the main is the usual case, and our low lying block drainage guide covers how that layout works. If the site has a basement car park or carries real flow, look at the Kwikflo dual stormwater station or browse all packaged pump stations.
Frequently asked questions
Can stormwater go into the sewer in Australia?
No, stormwater generally cannot go into the sewer in Australia. Water authorities treat it as an illegal cross connection because rain overloads sewer mains and causes overflows. Your licensed plumber can confirm the rules for your authority.
Can I use a sewer pump for stormwater?
Yes, a sewer cutter pump will physically move stormwater, but it is the expensive way to do it, and grit wears the cutter. A drainage pump is the correct choice for stormwater. Using a stormwater pump on sewage is the mistake to avoid, because rags and solids will block it.
Can one pump station take both sewage and stormwater?
No, one pump station should not take both sewage and stormwater. Once the two mix in a tank the contents are sewage, and they would have to discharge to sewer, which is the connection authorities prohibit. A site with both needs two separate stations.
What is the difference between stormwater and sewer in Australia?
Stormwater is rain from roofs and hard surfaces, usually discharged to council drainage. Sewer carries waste from toilets, showers, sinks and laundries to the water authority's treatment system. They are separate networks, with separate pipes and separate rules.
Do I need approval for a stormwater or sewer pump station in Australia?
Most pump station work needs a licensed plumber, and approvals depend on your state, your council and your water authority. Sewer work is normally regulated plumbing work. Your plumber will know what applies to your site and should confirm it before you order.
Not sure which one your site needs?
Send us a sketch or a plan, what needs pumping, the height and the distance, and we will tell you which station fits. Contact us here or get a sewer or stormwater station quote. Plumbers and builders can also ask about trade pricing.
Shop all sewage and stormwater pump stations →
This guide is general information for Australian conditions and isn't a substitute for advice from a licensed plumber. Pump station installation and sewer connection are regulated work, and requirements differ between states and water authorities. Have your plumber confirm sizing, approvals and compliance before you order.