VS Series
South West Water v Thames Water
Two regulated water companies, one in the South West and one in London and the Thames Valley. How do their accounts compare?
Thames Water leads on three of the five measures that matter most: turnover, pre-tax profit, profit margin, growth and net assets. Thames Water is the biggest by turnover at £3,757m, against £939m at South West Water. South West Water keeps more of every £100 it takes, £13.30 as pre-tax profit.
The year ends are close enough to compare like for like. Thames Water files group accounts that include subsidiaries; South West Water files for a single company, which flatters the group on size.
Accounts compared: South West Water to Mar 2026 · Thames Water to Mar 2026
Who they are
South West Water
South West Water Limited · 02366665South West Water provides water supply and sewerage services to homes and businesses in Devon and Cornwall, with parts of Dorset and Somerset.In brief: water and sewerage · Devon and Cornwall · Ofwat-regulated bills · owned by PennonFull profile →Thames Water
Thames Water Utilities Limited · 02366661Thames Water is the water and wastewater company for London and the Thames Valley, supplying drinking water and collecting and treating sewage.In brief: water and wastewater · London and Thames Valley · regulated bills · privatised 1989Full profile →The Numbers
The leader on each measure is marked. Movements are against each company's own prior year. Pre-tax profit is filed except where marked (est.).
Category winners
Biggest by turnover
Thames Water
£3,757m
Most pre-tax profit
Thames Water
£226m
Highest profit margin
South West Water
13.3%
Fastest-growing turnover
Thames Water
+37.2%
Biggest employer
Thames Water
8,472 staff
Highest pay per head
Thames Water
£71,000
Most turnover per head
Thames Water
£443,000
Largest net assets
South West Water
£1,084m
Most cash
Thames Water
£557m
The Takeaway
- South West Water converts the most of its turnover. Of every £100, £13.30 reaches pre-tax profit, against £6.03 at Thames Water.
- Thames Water is the largest on the top line, £3,757m of turnover, 4.0x South West Water's £939m.
- Thames Water is growing fastest, turnover +37.2% on its own prior year.
- Thames Water is the biggest employer with 8,472 people; Thames Water pays the most per head, an average staff cost of about £71,000.
- South West Water has the largest balance sheet, net assets of £1,084m, while Thames Water holds the most cash at £557m.
Who keeps the most of every £100 of sales?
South West Water keeps the most: £13.30 of every £100 of turnover becomes pre-tax profit. Thames Water keeps the least, £6.03.
Financing bites hardest at Thames Water: £22.14 of every £100 goes on interest.
Every profit figure here is the one the company filed.
The chart splits each company's turnover into £100: what goes on people, on interest and on everything else, and what is left as profit.
Out of every £100 of turnover
Each column is £100 of that company's own turnover, so companies of any size compare on one scale; the figures are pounds out of each £100, not millions. Companies run from the best margin to the worst. Payroll is staff costs, financing is interest paid, other running costs are everything else, and profit is pre-tax profit, filed or estimated as marked in the table. A loss is not an extra cost: it is the part of the costs that runs past the £100 line, marked with a red bracket. Hover over any segment for its figure.
Who is the biggest, and does the comparison hold?
By turnover the order is Thames Water (£3,757m), South West Water (£939m).
By headcount, Thames Water leads with 8,472 employees.
The accounting periods all end in the same month. The bases differ: group accounts include the businesses a company owns, single-company accounts do not.
Turnover on the latest filing
Who is growing fastest?
Thames Water grew fastest, turnover +37.2% on its own prior year, ahead of South West Water (+27.1%).
Turnover change on each company's own prior year
Who employs the most, who pays the most, and who brings in the most per head?
Thames Water employs the most, 8,472 people, against 2,695 at South West Water.
Thames Water has the highest average staff cost, about £71,000 a head; South West Water the lowest, about £56,000.
Thames Water brings in the most turnover per employee, about £443,000, against £348,000 at South West Water. It says as much about the business model as the workforce: a marketplace or a wholesaler needs far fewer people per pound than a restaurant or a gym.
Who owns each one?
Ownership as recorded on the Companies House register of people with significant control, in the bands the register uses.
Held by Pennon Group Plc
A company recorded as a person with significant control. 2 outstanding charges on the register.
Who owns South West Water →
Thames Water Utilities Limited · 02366661Held by Thames Water Utilities Holdings Limited
A company recorded as a person with significant control. 7 outstanding charges on the register.
Who owns Thames Water →
What does the full ledger show?
| Measure | South West Water | Thames Water |
|---|---|---|
| Registered name | SOUTH WEST WATER LIMITED | THAMES WATER UTILITIES LIMITED |
| Company number | 02366665 | 02366661 |
| Incorporated | 1989 | 1989 |
| Accounts filed | 7 August 2026 | 3 September 2026 |
| Turnover, prior year | £739m | £2,738m |
| Pre-tax profit, prior year | -£61m | -£1,647m |
| Staff costs | £152m | £605m |
| Payroll share of turnover | 16.2% | 16.1% |
| Employees, prior year | 2,777 | 7,824 |
| Dividends paid | n/d | n/d |
| Charges outstanding | 2 | 7 |
A figure the filing does not disclose is shown as n/d; a zero in a filing is treated as not disclosed. Rounding: below £0.1m in thousands, £0.1m to £2m to one decimal place, above that to the nearest million.
South West Water v Thames Water: common questions
Who is the biggest of South West Water or Thames Water?
Thames Water, with turnover of £3,757m in the year to March 2026.
Which makes the most profit?
Thames Water: £226m pre-tax in the year to March 2026.
Which employs the most people?
Thames Water, with 8,472 employees in its latest accounts.
South West Water or Thames Water: which is bigger?
Thames Water, with turnover of £3,757m against £939m at South West Water on their latest filings. On margin, South West Water keeps more of each £100 as pre-tax profit. The full head to head is in the VS Series. Read the VS page →
Where do these figures come from?
Each company's latest accounts filed at Companies House. Each links to its full Spark Intel profile, which names the filing it comes from.
Deep dive: what story does Thames Water's money tell? →
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