Why Does My Toilet Keep Running? A Singapore Homeowner’s Guide

TL;DR

A toilet that runs non-stop is almost always one of three parts failing: the flush valve seal, the fill valve, or the float. None of them are expensive. What is expensive is leaving it. PUB states a leaking cistern can waste up to 10 litres of water an hour, which works out to roughly 240 litres a day and around $23 a month on your water bill at current rates. Test it in two minutes with food colouring in the cistern. If colour appears in the bowl without flushing, the flush valve seal has gone.

The short answer

Your toilet is running because water is escaping from the cistern into the bowl faster than the fill valve can shut off, or because the fill valve never gets the signal to stop. The three usual culprits are a worn flush valve seal, a faulty fill valve, and a float set at the wrong height or waterlogged.

This matters more in Singapore than most people assume, because the water is metered and the leak is silent. A dripping tap announces itself. A running cistern just quietly adds a few dollars a week to a bill you probably do not read line by line.

The two-minute test that tells you which part failed

Put a few drops of food colouring into the cistern tank, then leave the toilet alone for fifteen minutes. Do not flush.

If coloured water appears in the bowl, water is passing from the tank into the bowl and your flush valve seal has failed. If the bowl stays clear but you can still hear water running, the problem is on the supply side: the fill valve or the float.

This is PUB’s own recommended check, published in its guidance on finding leaks, alongside the broader meter test. Turn off every tap and appliance in the flat, then look at your water meter. If the dial is still moving, water is going somewhere it should not, and a running cistern is one of the first places to look.

The three things that actually fail

The flush valve seal

This is the most common by a wide margin. The flush valve is the outlet at the bottom of the cistern, and it is closed by a rubber seal or flapper. Rubber perishes. In Singapore’s climate it perishes faster than the manufacturer’s estimate, and the seal does not fail cleanly. It goes slightly soft, seats slightly imperfectly, and lets a thin continuous stream past.

That is why the classic symptom is a toilet that runs quietly and constantly rather than one that obviously floods. The seal is a low-cost part and the replacement is quick. If a plumber tells you the whole cistern needs replacing because the seal has gone, get a second opinion.

The fill valve

The fill valve, sometimes called the inlet valve or ballcock, refills the tank after a flush and shuts off at the set level. When its internal diaphragm wears, it either fails to shut off completely or shuts off and then weeps back open. You get a cistern that refills in short bursts every few minutes, which is the sound most people describe as the toilet “topping itself up”.

The float

The float tells the fill valve when to stop. Two things go wrong. It gets knocked or set too high, so water rises above the overflow tube and drains continuously into the bowl. Or, on older ball-float systems, the ball itself develops a pinhole, fills with water, sits lower than it should, and never signals the valve to close.

The float is the cheapest fix on this list and often needs adjustment rather than replacement.

What a running toilet actually costs you in Singapore

This is the part most guides skip, so here are the real numbers.

PUB’s figure is that a leaking cistern wastes up to 10 litres per hour. That is 240 litres a day, or about 7.2 cubic metres a month.

Singapore’s domestic water price, as revised on 1 April 2025 and still in force, is $1.43 per cubic metre for the tariff, plus a Water Conservation Tax at 50% of the tariff, plus a waterborne fee of $1.09. That comes to $3.24 per cubic metre before GST for households using up to 40 cubic metres a month. Above 40 cubic metres, every component steps up and the total becomes $4.39. You can check the current structure on PUB’s water price page.

So at PUB’s own leak rate:

Those figures exclude GST at 9%, and they assume you stay inside the lower tariff band.

Here is the point nobody makes, and it is the reason we push customers to fix this quickly. A four-person household in a flat already sits somewhere in the region of 15 to 20 cubic metres a month. Add 7 to 12 cubic metres of leak on top and you can cross the 40 cubic metre threshold. The moment you do, the marginal cost of every additional cubic metre jumps from $3.24 to $4.39, a rise of about 35%. The leak does not just cost you the water it wastes. It can reprice the water your family was going to use anyway.

That is the honest argument for fixing a running toilet this week rather than next month, and it is a stronger one than any plumber’s sales pitch.

Do you need a licensed plumber for this?

No, and we would rather say so plainly.

PUB requires a Licensed Plumber for regulated water service and sanitary work, and since 1 April 2018 it has been an offence to engage an unlicensed plumber for that work. But PUB also publishes a list of simple plumbing works that do not require a licence, and servicing flushing cistern components is on that list, alongside replacing taps and clearing blockages.

So a competent handyman can legally replace your flush valve seal. Where the requirement bites is if the job turns out to need the sanitary pipework altered or the toilet bowl removed and reinstalled. That is regulated work, and it needs a licensed plumber. If you want the background on where that line sits, our toilet bowl repair page sets it out in more detail.

What we check first, and in what order

After enough of these, the order stops being a diagnostic tree and becomes muscle memory.

We listen before we open anything. A continuous hiss points to the fill valve. Silence with water visibly moving in the bowl points to the flush valve seal. An intermittent refill every few minutes usually means a slow seal leak that drops the tank level just enough to trigger the fill valve, which is the same fault presenting differently.

Then we lift the lid and look at the water level against the overflow tube. If water is running over the top of that tube, the problem is the float or the fill valve, and we have not needed to touch the flush valve at all.

The mistake we see most often, and it is usually a well-meaning DIY attempt, is replacing the whole flush mechanism when only the seal had perished. The parts get thrown away, the labour doubles, and the underlying issue, which is often that the cistern was never adjusted correctly after a previous repair, comes back.

One opinion, clearly ours: if your cistern internals are original and the toilet is past about ten years old, replacing the seal alone is a false economy. Once one rubber component has perished, the others are the same age and in the same climate. We will tell you the cost of doing the set now against the likelihood of a second call-out inside a year, and let you choose.

A note on new toilets and flush volumes

If you are replacing a toilet rather than repairing one, Singapore regulates how much it may flush.

Under the Mandatory Water Efficiency Labelling Scheme, every dual-flush low-capacity cistern supplied in Singapore has been required to carry a minimum 2-tick rating since 1 April 2019. In practice that caps a new full flush at 4.0 litres and a reduced flush at 3.0 litres. Since 1 January 2022, WC flush valves fall under the same scheme with the same 4.0 litre ceiling, and from 1 January 2023 all installed flush valves must meet the 2-tick minimum. A 3-tick product goes further, to 3.5 litres full and 2.5 litres reduced.

The practical effect is that a modern replacement uses meaningfully less water per flush than a cistern from the 2000s, which changes the repair-or-replace arithmetic on a very old toilet.

When it is not the toilet at all

If your bill has jumped and the toilet checks out clean, the leak is elsewhere. The meter test is the fastest way to confirm water is escaping somewhere in the flat, and from there it is usually a concealed pipe, a weeping connection under a sink, or a failing flexible hose. Concealed leaks need locating before anything is opened up, which is a different job from a cistern repair. Our pipe leak repair service covers how that detection works.

Frequently asked questions

How much does it cost to fix a running toilet in Singapore?
A flush valve or fill valve repair sits at the low end of plumbing work, generally in the same band as a tap replacement rather than anything structural. Published Singapore guides put comparable small repairs in the $80 to $200 range, and the part itself is a small fraction of that. Ask whether the quote is GST-inclusive before agreeing, because practice varies between firms.

Can I fix a running toilet myself?
Legally, yes. PUB lists servicing flushing cistern components among the simple works that do not require a licensed plumber. Practically, replacing a flush valve seal is within reach for most people with a spanner and patience. The two things that catch people out are buying a seal that does not match the cistern model, and overtightening plastic components on reassembly, which cracks them.

Why does my toilet run for a few seconds every few minutes?
That is called phantom flushing, and it means the tank is slowly losing water into the bowl until the level drops far enough to trigger the fill valve. The fill valve is doing its job correctly. The flush valve seal is the part that has failed.

Is a running toilet an emergency?
No. It is not going to flood your flat, and it can wait for a normal appointment rather than an after-hours call-out that carries a surcharge. It is a this-week problem, not a tonight problem. The cost of waiting is the water, not the risk.

My toilet runs and also drains slowly. Same problem?
No, those are two separate faults that happen to share a fixture. Running water is a cistern fault on the supply side. Slow draining means the discharge side is restricted, which is a choke and needs clearing rather than a cistern repair. If you have both at once, expect two fixes, and ask for both to be quoted separately.

How do I know if the leak is the toilet or somewhere else?
Turn off every tap and appliance and watch your water meter. If it is still moving, you have a leak somewhere. Then do the food colouring test on each toilet in the flat. If the colour appears in a bowl, you have found it. If every toilet is clean and the meter still moves, the leak is in the pipework.

Will fixing it actually show up on my bill?
Yes, and quickly. Water is billed by volume, so removing a 200 to 400 litre daily loss shows in the next billing cycle. If your household was sitting near the 40 cubic metre threshold, the saving is larger than the raw volume suggests, because you drop back into the cheaper band.

Quick answers

Should I repair or replace a toilet that keeps running?
Repair, in most cases. The failing parts are inexpensive and the fault is rarely the bowl or cistern body. Replacement makes sense when the cistern is cracked, when the model is old enough that matching parts are hard to source, or when the toilet is old enough that a modern 2-tick or 3-tick unit would cut your flush volume meaningfully.

How urgent is it really?
Fix it within the week. At PUB’s own leak figure it is costing roughly $23 a month, and there is a threshold effect that can make it cost more than that if it pushes your household into the higher tariff band.

What should I ask a plumber before they start?
Ask what they think has failed and what the part costs, ask whether the quote includes GST, and ask whether they will replace the single failed component or the whole mechanism. A plumber who cannot tell you which of the three parts is at fault before opening the cistern has not diagnosed it yet.

Get it looked at

A running toilet is one of the cheapest problems in the house to fix and one of the most expensive to ignore. If yours has been running for weeks, it has already cost more than the repair.

Send us a photo of the cistern with the lid off on WhatsApp at +65 9199 0308 and we can usually tell you which part has gone before we arrive. You can also see our published plumbing prices or get in touch here.

Sources: PUB, Useful Tips on Finding Leaks; PUB Water Price (rates effective 1 April 2025); PUB Plumbing Works and the Licensed Plumber requirement; PUB Mandatory Water Efficiency Labelling Scheme. Water cost figures are calculated from PUB’s published tariff components and exclude GST. Repair price ranges are indicative market ranges drawn from published Singapore plumbing guides, not a regulated schedule.