How Unmetered Water Billing Works
If you don't have a water meter, you're being charged based on the rateable value of your property. This is an outdated system that dates back to when water meters weren't common. Your rateable value was originally determined decades ago and has no relationship to how much water you actually use.
Think of it like this: it's as if your electricity bill was based on the size of your house rather than how much electricity you actually consume. You could be an energy-conscious household that barely uses any power, but you'd still be charged the same as your neighbour who leaves lights on 24/7—simply because your houses are similar sizes.
That's exactly what's happening with unmetered water billing.
The Problem: Paying for Water You Don't Use
Here's where it gets interesting—and potentially expensive. Because your water bill is based on your property's rateable value rather than consumption, you could be paying for far more water than you actually use.
According to average consumption data from Southern Water, households use varying amounts of water depending on how many people live there:
- 1 person: 85 m³ per year on average
- 2 people: 110 m³ per year on average
- 3 people: 135 m³ per year on average
- 4 people: 150 m³ per year on average
- 5 people: 165 m³ per year on average
- 6 people: 180 m³ per year on average
But your unmetered bill doesn't care how many people live in your home. It only cares about your property's rateable value.
When Does Metered Water Make Sense?
This is where our Portsmouth Water Calculator becomes useful. It calculates the maximum amount of water you can consume while still paying less than you currently do on an unmetered supply.
Here's the crucial insight: if your rateable value matches a larger household size than you actually have, you could save significant money by switching to a metered supply.
For example, if you're a single person or a couple living in a property with a high rateable value, you're effectively being charged as if you're a much larger household. You could be paying for a family of six's water consumption when you're only using enough for one or two people.
The Rateable Value Sweet Spots
Based on 2025 tariffs from Portsmouth Water and Southern Water, here are the maximum rateable values where switching to metered water makes sense for each household size:
- 1 person household (85 m³): Rateable value up to £145
- 2 people household (110 m³): Rateable value up to £194
- 3 people household (135 m³): Rateable value up to £226
- 4 people household (150 m³): Rateable value up to £258
- 5 people household (165 m³): Rateable value up to £274
- 6 people household (180 m³): Rateable value up to £306
If your rateable value is higher than the threshold for your household size, switching to metered water could save you hundreds of pounds per year—even if you use slightly more than average water consumption.
Who Does This Apply To?
This calculator is specifically designed for customers in the Portsmouth Water supply area, which includes:
- Portsmouth
- Gosport
- Fareham
- Havant
- Chichester
- Bognor Regis
If you live in any of these areas and don't currently have a water meter, this tool could reveal whether you're overpaying for water.
Check for "Opportunistic Meters"
Here's something many people don't know: Portsmouth Water sometimes installs what's called an "opportunistic meter" when they're carrying out repair works in your street. This means you might already have a meter outside your property without realising it.
If an opportunistic meter has been installed, you could switch to metered billing immediately without waiting for a meter installation appointment. It's worth checking outside your property or calling Portsmouth Water to ask.
How to Use the Calculator
Using our Portsmouth Water Calculator is straightforward:
- Find your rateable value: Check your water bill or council tax documents for this number.
- Enter it into the calculator: The tool accepts values between £1 and £700.
- Review the results: You'll see your current unmetered cost, the maximum water you can use while still saving money, and comparisons for different household sizes.
The calculator shows you exactly how much money households of different sizes would pay on a metered supply, based on average consumption data. This helps you see whether switching makes financial sense for your situation.
What If I Can't Get a Meter Fitted?
In some properties, it's not practical or possible to install a water meter. If that's your situation, you may be eligible for an assessed bill, which charges you based on the number of occupants and/or bedrooms in your home rather than your rateable value.
This is fairer than rateable value billing because it's based on realistic water consumption rather than an arbitrary property value. Contact Portsmouth Water or Southern Water to discuss this option if a meter can't be fitted.
Additional Support for Low-Income Households
If you're on a low income or receive certain benefits, you may qualify for reduced water tariffs:
Social Tariff
If your household income is at or below £21,000 (excluding certain benefits like housing benefit, DLA, and pension credit), you could qualify for the social tariff, which caps your water supply charges at £123.58 and sewage at 45% of supply for 2025.
WaterSure Tariff
If you have three or more children under 19, or someone in your household has a medical condition requiring significant water use, you may qualify for the WaterSure tariff—provided you also receive certain benefits. This caps your bills at specific amounts and requires a water meter.
Both Portsmouth Water and Southern Water offer these tariffs. Check the calculator tool for application links and full eligibility criteria.
The Bottom Line
Unmetered water billing made sense decades ago when meters weren't common. Today, it's an outdated system that can leave many households—particularly smaller ones or those in larger properties—paying far more than they should.
The good news is that switching to a metered supply is usually free, and Portsmouth Water allows you to switch back to unmetered billing within 12 months if you find you're not saving money.
Before making any decision, use our free calculator to see if switching makes sense for your household. It takes less than a minute to check, and you might discover you've been overpaying by hundreds of pounds per year.