Lesson 2 of 3 Math checked Last reviewed 16 June 2026 14 min

Water and waste economics: regulated returns, tariffs, desalination and routes

How a regulator builds a water bill, what desalinated water really costs, why leaks and route density matter, and how landfill taxes push waste toward recycling.

Industry brief, with a one-minute summary: Water, waste and utilities

Key takeaways

A regulated water company does not choose its prices.
Every cubic metre that leaks has already been pumped and treated, and in the Gulf it may have been desalinated at close to USD 0.5.
The regulator's sum is called the building block method.

Key idea

A regulated water company does not choose its prices. The regulator adds up what an efficient company should spend to run the network, a charge for the wear of its assets, and a fair return on the money invested, and turns the total into a bill. The company earns more only by spending less than allowed, performing better than targets, or growing the asset base the return is paid on.

The regulator's sum is called the building block method. Allowed revenue equals operating costs, plus depreciation of the asset base (in England and Wales called run-off), plus the allowed return times the asset base. For 2025 to 2030, Ofwat allowed the companies in England and Wales about GBP 104 billion of total spending and a return of 4.03 percent a year after inflation; in March 2026 the Competition and Markets Authority raised it to 4.20 percent for five companies that appealed.

Worked case

Building a regulated water bill from its blocks

The prompt

Riverbend Water (a fictional company in England) has a regulatory capital value of GBP 10 billion. The regulator allows operating costs of GBP 800 million a year, run-off (depreciation) of GBP 400 million a year and a return of 4.03 percent a year. It bills 2.5 million households. What is its allowed revenue, and the average bill per household? Then recompute the bill with a return of 4.20 percent.

Open this case to practice it with a partner

The structure

Allowed revenue = operating costs + run-off + allowed return x asset base
- Return on capital = asset base x allowed return
- Allowed revenue = operating costs + run-off + return on capital
- Average bill = allowed revenue divided by households billed

Working it through

1. Return on capital
4.03 percent of GBP 10,000 million.
Return on capital (GBP million):10,000 × 0.0403 = 403
2. Allowed revenue
GBP 800 million plus 400 plus 403.
Allowed revenue (GBP million):800 + 400 + 10,000 × 0.0403 = 1,603
3. Average bill
GBP 1,603 million over 2.5 million households.
Average bill (GBP per household):1,603 ÷ 2.5 = 641
4. Bill with a 4.20 percent return
The return becomes GBP 420 million, so revenue is GBP 1,620 million.
Average bill at 4.20 percent (GBP per household):(800 + 400 + 10,000 × 0.042) ÷ 2.5 = 648

The recommendation

Riverbend's bill of about GBP 641 a household is mostly set by the regulator, so its profit plan should focus on beating the cost allowances and on the return, not on price. First, the return on capital is GBP 403 million of the GBP 1,603 million, so a change of 0.17 points in the allowed return moves the bill by about GBP 7. Second, every GBP 1 million saved below the operating allowance adds to profit until the next review. The risk is fines for leaks and sewage spills. As a next step, compare its cost per household with the most efficient companies.

Risks: Missing performance targets (leaks, pollution) brings penalties; Heavy borrowing makes the company fragile if interest rates rise, as the case of Thames Water showed.

Desalination: what a cubic metre costs

Most new plants use reverse osmosis: seawater is pushed at high pressure through membranes that hold back the salt. It needs far less energy than the older thermal plants that boil seawater, which is why the Gulf has shifted to it. The cost of a cubic metre comes from three blocks: the capital charge on the plant, energy, and other running costs (membranes, chemicals, staff). Recent Saudi tenders have been won at about USD 0.41 to 0.46 per cubic metre: about 0.41 for Jubail 3A in 2020 and about 0.46 for Rabigh 4 in 2023, according to the developer and trade press.

Worked case

The cost of a cubic metre of desalinated water, and why energy prices matter

The prompt

A developer is bidding for a 300,000 cubic metre a day reverse osmosis plant on the Red Sea coast of Saudi Arabia. It will cost USD 300 million to build, and the developer uses a capital recovery factor of 8 percent a year (the yearly payment that repays the plant and its financing). The plant runs 95 percent of the time. It uses 3.5 kWh of electricity per cubic metre at USD 0.04 per kWh. Other running costs are USD 0.08 per cubic metre. What is the cost per cubic metre? What if the electricity price doubles? (Figures are illustrative.)

Open this case to practice it with a partner

The structure

Cost per cubic metre = capital charge + energy + other running costs
- Yearly output = daily capacity x 365 x availability
- Capital charge = capex x capital recovery factor, divided by yearly output
- Energy = kWh per cubic metre x price per kWh

Working it through

1. Yearly output
300,000 cubic metres a day, 365 days, 95 percent of the time.
Yearly output (cubic metres):300,000 × 365 × 0.95 = 104,025,000
2. Capital charge per cubic metre
USD 24 million a year (8 percent of 300 million) spread over the yearly output.
Capital charge (USD per cubic metre):300,000,000 × 0.08 ÷ 104,025,000 = 0.2307
3. Energy per cubic metre
3.5 kWh at USD 0.04.
Energy cost (USD per cubic metre):3.5 × 0.04 = 0.14
4. Total cost
Capital, energy and other running costs added.
Total cost (USD per cubic metre):300,000,000 × 0.08 ÷ 104,025,000 + 3.5 × 0.04 + 0.08 = 0.4507
5. Total cost if electricity doubles
Energy becomes 3.5 kWh at USD 0.08, which is USD 0.28.
Total cost with dearer power (USD per cubic metre):300,000,000 × 0.08 ÷ 104,025,000 + 3.5 × 0.08 + 0.08 = 0.5907

The recommendation

The developer can bid near USD 0.45 per cubic metre only if it locks in cheap power, because energy is about a third of the cost and doubling its price lifts the total to about USD 0.59, a rise of about 31 percent. First, the capital charge of about USD 0.23 is fixed once the plant is financed. Second, energy is the block most exposed to change, so a long power contract or its own solar supply matters. The risk is a tariff set too low to cover membranes and repairs. As a next step, price a solar power purchase agreement for the plant.

Risks: Plant downtime lowers yearly output and raises the capital charge per cubic metre; The brine left over must be handled so it does not harm the sea.

Waste: routes, gate fees and landfill taxes

A collection truck with its crew costs about the same each day whether it stops at 800 homes or 1,200. So the cost per home depends on route density: how many homes it serves per hour. After collection, the waste goes wherever the total cost is lowest: the gate fee (the price a plant or landfill charges per tonne) plus transport, plus any tax. Landfill taxes, such as the UK standard rate of GBP 130.75 per tonne from April 2026, make burying waste dearer and push it toward recycling and energy recovery.

Timed math drill

A waste truck and crew in a US city cost USD 800 a day. The truck works 5 days a week and collects from 1,000 homes a day, so it serves 5,000 homes once a week. What is the collection cost per home per year, in USD? (Use 52 weeks.)

Timed math drill

A council in England sends 100,000 tonnes of waste a year to landfill, taxed at GBP 130.75 per tonne. If it moves 20 percent of that waste to recycling instead, how much landfill tax does it save each year, in GBP?

Leaks are lost money and lost water

Every cubic metre that leaks has already been pumped and treated, and in the Gulf it may have been desalinated at close to USD 0.5. Cutting non-revenue water is often the cheapest new source of water a city has, because it needs no new plant. When a case asks for more water supply, check leaks and unbilled water before building.

Check your understanding

A regulated water company wants to earn more profit within a five-year price period. Which is the most realistic lever?

Terms in this lesson

Rate base Cost of capital (WACC)Depreciation and amortization Capex (capital expenditure)Opex (operating expenses)Fixed cost Unit economics Sensitivity analysis Economies of scale Capacity utilization

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