What a leak allowance covers, and what it does not
A leak allowance credits the volumetric charge for water that leaked away rather than being used. It does not usually cover the cost of the repair, and whether it credits the sewerage element as well as the water element roughly doubles what is at stake, which is why that is the question to ask first.
Last reviewed 14 August 2026
The short answer
A bill for a leak has two volumetric parts and a fixed part, and an allowance touches at most two of the three.
| Part of the bill | Covered by an allowance? |
|---|---|
| The volumetric water charge on the leaked volume | Usually. This is the core of what an allowance is. |
| The volumetric sewerage charge on the leaked volume | Sometimes, and it is worth asking specifically. It can be comparable in size to the water element. |
| The standing charge | Not applicable. It is fixed, so a leak never increased it in the first place. |
| The cost of the repair | Usually not. That is a separate policy where one exists at all. |
The third row is not an exclusion. A standing charge does not rise because of a leak, so there is nothing there to credit, and an allowance that appeared to cover it would mean something else had gone wrong.
How this works in practice
For a supply pipe leak, there is a question worth asking before the allowance question, and it is a stronger one.
The argument has three parts and they are not equally strong, so they are worth separating before anybody uses it.
| Part | Status |
|---|---|
| Companies describe the sewerage charge as being for water returned to the sewer. Thames Water writes of "wastewater returned to our sewers", United Utilities of water "not returned to the sewer", and Yorkshire Water of what "returns to the sewer". | Quoted from their own published charges schemes. Read directly. |
| Water lost from a buried supply pipe soaks into the ground and does not return to a sewer. | A deduction from the above, and not seriously arguable. |
| Whether your company's scheme therefore gives you a RIGHT to have that charge removed, or whether the only route is the discretionary allowance. | NOT ESTABLISHED. This site has read six charges schemes for how the sewerage charge is calculated, and none of the twenty-two for this question. |
So the defensible position is a question rather than a claim: here is the basis your company states for the charge, here is why a supply pipe leak does not meet it, what does your scheme say. That is much stronger than asking for a discretionary credit and it cannot be knocked down. What it is not is "you should not have been charged and you are owed a refund", because that asserts a term nobody here has read.
- Establish where the leak was first, because the whole argument rests on it being on the supply pipe rather than inside.
- Ask about the sewerage element separately from the allowance. They may be handled by different parts of the same company.
- Ask about the allowance for the water element as well, since the two are not alternatives.
The mechanics of how sewerage volume is calculated matter here, because companies do not all bill the same share of metered volume. how the sewerage half of the bill is calculated sets out the two mechanisms.
What changes the answer
Four things, and every one of them is set by your own company rather than nationally.
- Which pipe leaked. Supply pipe leaks are the usual case an allowance exists for; internal leaks are more often excluded or discretionary, because a household could in principle have found one.
- Whether it is your first, and whether your company's policy grants a repeat at all.
- Whether you repaired it in time. A stated window from discovery is common, and missing it can void an otherwise valid claim.
- How long the leak ran. The credit usually covers a stated period rather than the whole history, so an early find is worth more than the water alone.
None of those is a national rule, which is why this site links every company's own policy rather than describing a typical one. There is no typical one.
Assumptions and sources
Drip Calculator: how much water does a leaking faucet waste?
United States Geological Survey, Water Science School · primary source
- Faucet drip volume, adopted: 0.25 ml
- Faucet drip volume, measured range: 0.2 to 0.33 ml
- Bath tap drip volume: 0.5 ml
- Drips per US gallon: 15140 drips
- Drips per litre: 4000 drips
The pharmacopoeial metric drop, 20 drops to 1 millilitre
United States Pharmacopeia, British Pharmacopoeia and European Pharmacopoeia convention · primary-standard source
- Standard drop volume: 0.05 ml
Tate's law: the weight of a falling drop
Thomas Tate, Philosophical Magazine, 1864, with the later drop-weight literature · primary source
- Drop weight: W = 2 * pi * r * gamma equation
Plumbers shine the spotlight on dripping taps during Water Saving Week
WaterSafe, with Waterwise · untraceable source
- Claimed annual waste from a dripping tap: 5500 litres per year
International Organization of Legal Metrology · primary-standard source
- MPE, accuracy class 2, lower zone Q1 to Q2: 5 %
- MPE, accuracy class 2, upper zone Q2 to Q4: 2 %
- MPE, accuracy class 1, lower zone: 3 %
- MPE, accuracy class 1, upper zone: 1 %
- In-service MPE multiplier: 2 ratio
- Q2 / Q1: 1.6 ratio
- Q4 / Q3: 1.25 ratio
Aquadis+ DN15 and DN20 specification sheet
Itron · manufacturer source
- Q1 minimum flow rate, DN15, Q3 2.5, R160: 15.6 l/h
- Q2 transitional flow rate, DN15, Q3 2.5, R160: 25 l/h
- Q3 permanent flow rate, DN15: 2500 l/h
- Typical starting flow rate, DN15: 0.4 l/h
- Typical starting flow rate, DN20: 2 l/h
- Q1 minimum flow rate, DN20, Q3 4.0, R160: 25 l/h
- Flow rate at which accuracy is within +/- 5%, DN15: 3 l/h
- Flow rate at which accuracy is within +/- 2%, DN15: 5 l/h
- Minimum scale interval, DN15 and DN20: 0.02 l
Water resources 2024 to 2025: analysis of the water industry's annual water resources performance
Environment Agency · primary source
- Household per capita consumption: 136.5 l/person/day
- Household per capita consumption, prior year: 137 l/person/day
- Household per capita consumption, dry-year adjusted: 140.3 l/person/day
- National leakage: 2617 Ml/day
- National leakage as share of water put into supply: 19 %
PR24 common performance commitments: per capita consumption (PCC), version 2.1
Ofwat · primary-standard source
- PCC formula: (measured household consumption + unmeasured household consumption) / total household population l/person/day
Leaky loos, why it's not as simple as faulty flush valves
ech2o, reporting research attributed to Thames Water · secondary source
- Toilets inspected: 58551 toilets
- Toilets found leaking: 4854 toilets
- Prevalence: 8.3 %
- Average residential leak rate: 400 l/day
- Average commercial leak rate: 2100 l/day
- UK-wide average across all WCs, leaking and sound: 20 l/day
- Share of leaking toilets with flush valves rather than siphons: 81 %
Waterwise · untraceable source
- Single leaking toilet: 215 to 400 l/day
- Share of toilets leaking: 5 to 8 %
- UK total from leaking toilets: 400000000 l/day
Methods for Calculation of Evaporation from Swimming Pools and Other Water Surfaces
M. M. Shah, ASHRAE Transactions SE-14-001 · primary source
- Outdoor unoccupied pool evaporation: E0 = (C1 + C2 * u) * (pw - pa) / ifg kg/(m2*h)
- C1, SI: 235 constant
- C2, SI: 206 constant
Location-specific long-term averages, Wisley, Surrey
Met Office · primary source
- Annual mean daily maximum temperature: 15.41 degrees C
- Annual mean daily minimum temperature: 6.66 degrees C
- Annual rainfall: 667.92 mm
- Annual mean wind speed at 10 m: 5.06 knots
Discover Water, the water industry transparency site run with Water UK, Ofwat, CCW, the Drinking Water Inspectorate and Defra · primary source
- Average annual household bill, combined water and sewerage: 639 GBP
- Average annual household bill, water only: 309 GBP
- Average annual household bill, sewerage only: 330 GBP
SI Brochure: The International System of Units (SI), 9th edition (2019), version 4.01, June 2026
Bureau International des Poids et Mesures · primary-standard source
- cubic metre: coherent derived unit of the SI, Table 5 m3
- litre: non-SI unit, Table 8. 1 l = 1 L = 1 dm3 = 10^-3 m3 l or L
- bar: non-SI unit, Table 8. 1 bar = 0.1 MPa = 10^5 Pa bar
Authority URLs for the named entities in content/entities.ts
Various, see per-entity notes · primary source
WC flush volume: three UK instruments, not one
UK Statutory Instruments, Northern Ireland Statutory Rules, and Scottish Water · primary-standard source
- Maximum single flush, all three jurisdictions: 6 litres
- Dual flush, lesser flush maximum: two-thirds of the largest flush volume ratio
- England and Wales transitional maximum, 1 Jul 1999 to 1 Jan 2001: 7.5 litres
Per-event central heating top-up volume, derived
Derived by Q3 from Boyle's law and typical UK domestic expansion vessel specifications · derived source
- Water held in an expansion vessel: V_water = V * (1 - P0 / P), pressures absolute equation
- Typical top-up, 8 l vessel at 1.0 bar pre-charge, 0.5 to 1.5 bar: 1.6 litres
- Typical top-up, 8 l vessel at 0.75 bar pre-charge, 0.5 to 1.5 bar: 2.4 litres
- Typical top-up, 12 l vessel at 1.0 bar pre-charge, 0.8 to 1.5 bar: 2.4 litres
- Typical top-up, 8 l vessel at 1.0 bar pre-charge, 1.2 to 1.5 bar: 0.9 litres
- Realistic range: 0.9 to 2.5 litres
Monodispersed Bubble Generation Using Hydrophobic Orifices: The Extended Tate’s Law
Bo Liu, Hao Zhang and co-authors, ACS Omega 2024, 9(17), 18854 to 18861 · primary source
The shape described here is what these policies have in common rather than a reading of all twenty-two. No comparison of every policy text has been made, so this page describes the axes on which they vary and sends you to your own company for what applies to you.
No amount appears on this page. No supplier rate on this site has been verified, so any figure would be invented, and in any case what an allowance covers changes far more slowly than what it is worth.
What to do next
Three questions, in this order, and the second is the one most people never ask.
- Ask whether you qualify for an allowance on the water element, and what evidence is needed.
- Ask separately whether the sewerage element applies at all, if the leak was on the underground supply pipe. That is a different and stronger question than asking for a credit.
- Ask whether there is a free or subsidised first repair, which is a separate policy again.
All three go better with a measured rate and dates in hand. what a claim actually needs covers what to have ready.
Common questions
- Does it cover the repair?
- Usually not. An allowance is about the bill for the water, not the plumber. Some companies separately offer a free or subsidised first repair on the supply pipe as a matter of policy, which is a different thing with different terms, and being offered one is not being offered the other.
- Why does the sewerage element matter so much?
- Because it is billed at a rate comparable to the water rate, so a bill for a leak can be roughly twice what the water alone would be. An allowance that credits only the water half leaves the other half in place.
- My leak was on the underground supply pipe. Should sewerage have been charged at all?
- That is the question to put to your company, and it is a stronger one than asking for a discretionary allowance. Companies describe the sewerage charge in their own schemes as being for water returned to the sewer, and water lost from a buried pipe does not return to one. What this site cannot tell you is whether your company's scheme treats that as grounds for removing the charge or only as grounds for an allowance, because that is a term of each scheme and we have not read all twenty-two. Ask it as a question rather than as a demand.
- How far back does it go?
- It varies, and it is usually a stated period rather than the whole life of the leak. A leak that ran for two years before being found may be credited for a much shorter window, which is one reason finding a leak early is worth more than the water alone suggests.
- Can I get one twice?
- Check, because it is one of the axes these policies differ on. Where a policy grants a first leak and not a second, the reasoning is that once you know the pipe has failed you are on notice, which makes a second leak in the same property a materially different proposition. Whether yours works that way is a term of your company's scheme and this site has read none of the twenty-two for it.