Why Is My Water Bill So High? Plumbing Problems to Check
A sudden jump in your water bill is almost always caused by a leak or a running fixture, most often a leaking toilet, a dripping tap, or a hidden underground pipe. Most are fixable in a single visit once they're actually found.
The tricky part is that these leaks are rarely loud or obvious. A toilet that "sounds fine" can still be leaking hundreds of litres a day. A pipe under the lawn can leak for months before anyone notices a damp patch. This guide runs through every common cause, in order of how often we actually find them, plus how to check each one yourself before calling a plumber.
How Much Should a Melbourne Water Bill Actually Be?
South East Water's average annual bill for 2026–27 is $1,136, based on 150 kilolitres of usage a year, which works out to about $284 per quarterly bill, or the equivalent of roughly $95 a month. If your last bill was close to $284, you're tracking normal. If it was well above that, or well above your own bill from the same quarter last year, it's worth working through the checks below.
| Annual Bill | Per Quarterly Bill | |
|---|---|---|
| Average bill, 2026–27 | $1,136 | ~$284 (~$95/month equivalent) |
| Average bill, 2025–26 (last year) | $1,057 | ~$264 (~$88/month equivalent) |
| Small toilet leak (trickle) | $425+ | ~$106+ (~$35+/month equivalent) |
| Large toilet leak | $3,000+ | ~$750+ (~$250+/month equivalent) |
| Dripping tap | ~$100 | ~$25 (~$8/month equivalent) |
Monthly figures are for budgeting comparison only, since South East Water bills quarterly, not monthly.
Usage itself is charged in two tiers: $4.1047 per kilolitre for the first 440 litres a day, then $5.2373 per kilolitre above that. A leak that pushes daily use over 440L doesn't just add cost, it shifts your entire excess usage into the more expensive tier for the rest of the billing period.
One more thing worth knowing: South East Water already has the lowest average bill of any provider in metro Melbourne this year (the metro average is $1,158). If your bill looks high next to a friend's on a different provider, it's more likely usage, not pricing.
Where Does Household Water Actually Go?
On average, Melbourne households use about 40% of their water in the bathroom, 30% outdoors, 20% in the laundry, and 10% in the kitchen. The average person uses around 159 litres a day, against a Victorian government target of 150.
This split tells you where to look first. Outdoor usage jumped? Check the irrigation system or garden tap before anything else. Bathroom's the likely area? The shortlist is short: toilet, shower, or a bathroom tap. It also explains why a bathroom leak hits the hardest, since it's already the biggest single slice of the pie, so a fault there compounds fast.
Is Your Toilet Silently Leaking?
A leaking toilet is the single most common cause of an unexplained high bill, and it can run for weeks without making a sound.
South East Water's Paper Test
- Wait 30 minutes after the last flush so the back of the pan is dry.
- Place a piece of toilet paper flat against the back of the bowl.
- Leave it a few minutes. Don't use the toilet during this time.
- Wet or torn paper means water is leaking past the flush valve.
A toilet can also leak from its base if the seal has failed. That's a different repair to a running cistern, and not one to leave, since a broken base seal can let sewage seep under the floor. Our toilet plumbing page covers both faults.
Could a Dripping Tap Be Adding to Your Bill?
A dripping tap can waste up to 20,000 litres a year, roughly 55 litres a day, adding about $25 to every quarterly bill.
It sounds small next to a toilet leak, but it almost never fixes itself. The usual cause is a worn washer or cartridge, often a straightforward fix. Check every tap in the house, including outdoor taps and the one behind the washing machine, since these get forgotten. Full detail is on our leaking tap repair page.
Could You Have a Hidden Underground Pipe Leak?
A hidden pipe leak under the lawn, driveway, or slab wastes huge amounts of water with zero signs indoors. It's the most common cause of a genuinely large, unexplained spike. Look for:
- A patch of grass that's greener or growing faster than the rest.
- Damp or soft ground where it should be dry.
- Cracking or subtle movement in a driveway, path, or slab.
- Running water sounds when every tap and appliance inside is off.
These leaks need locating before they're fixed, since digging blind isn't practical. Leak detection uses acoustic equipment to pinpoint the exact spot, keeping the repair small instead of trenching the yard. More on our leak detection page. If the pipe has actually burst, see our burst pipe page for what to do in the meantime.
Check Your Hot Water System
Hot water systems can leak from the Pressure Temperature Relief Valve (PTRV), and because the unit usually sits where nobody walks, it can go unnoticed for a long time. Check the base and pipework for pooling water or a steady drip. In older systems, a faulty PTRV isn't just wasted water. It can let dangerous pressure build up inside the tank.
Other Less Common Culprits
Worth ruling out if the checks above come up clean:
| Source | What to look for |
|---|---|
| Irrigation / sprinklers | Unexplained wet patches or overly green sections in the garden |
| Evaporative cooling | Water running down the roof, or a wet ceiling patch when the unit is off |
| Pool / tank auto top-up | A float valve stuck open, topping up water that's already escaping elsewhere |
How to Check Your Meter for a Leak
If nothing above explains it, South East Water's own meter test is the most reliable way to confirm a leak anywhere on the property.
- Find your meter, usually near the front gate or fence, and note the reading.
- Turn off every tap and appliance, including the toilet cistern.
- Wait 20 minutes. Nobody uses any water.
- Check the meter again. If the numbers moved, there's a leak on your side of the meter.
If the test confirms a leak but you can't find it, that's the point to call a plumber rather than keep searching, especially if it might be under a slab or lawn.
Already Fixed the Leak, or Not Sure If You Need a Plumber?
Claiming back a fixed leak
South East Water's High Usage and Undetected Leak (HULA) review can waive or reduce the extra charges from a fixed leak.
- The leak must have been repaired within 2 weeks of being identified.
- The review request must be submitted within 90 days of the high bill or usage notification.
- You'll need a plumber's report confirming the leak and repair, plus a current meter reading.
When to call a licensed plumber
- The paper test confirms a toilet leak that DIY fixes don't stop.
- The meter test shows ongoing usage with everything off.
- You suspect an underground leak but can't locate it.
- The hot water system's PTRV is leaking, or the unit is 8 to 10+ years old.
Bill Spiked and Can't Find the Source?
DMACK Plumbing & Gas offers fast, same-day callouts across Pakenham and the surrounding suburbs, with upfront pricing and no surprise charges. If your bill has spiked and you can't find the source, we'll track it down properly the first time.
Contact DMACK Plumbing & Gas
