Description: A close up of someone’s hands as they count out coins. Photo by Towfiqu barbhuiya on Unsplash

Southern Water has secured the final £300 million of a £1.2 billion equity package, with most of the new capital coming from Asterion Industrial Partners. The Madrid-based infrastructure investor will join the Macquarie-led consortium as a minority shareholder with a stake of around 20%, subject to regulatory approval.

What the deal completes

The £300 million tranche finishes the £1.2 billion support package first announced in July 2025, of which Macquarie-managed funds committed £900 million during 2025. The latest investment brings total equity put into Southern Water since Macquarie acquired the business in 2021 to more than £2.8 billion. The capital is primary equity, meaning it goes into the company itself rather than to existing shareholders selling down.

Asterion, which manages around $10 billion in assets, described the deal as its entry into the UK water sector. Chief executive Jesús Olmos said the investment provides primary capital to help fund a significant capital programme focused on strengthening and modernising water infrastructure.

Where the money goes

The funding supports Southern Water’s capital programme for 2025 to 2030, which the company calls its largest to date. Investment priorities include reducing storm overflow discharges, improving river and coastal water quality, upgrading treatment assets, and strengthening resilience across water supply and sewerage networks. The company says it deployed £1.1 billion over the year to March 2026 as the programme began.

A turnaround still under scrutiny

Southern Water serves millions of people across Hampshire, the Isle of Wight, West Sussex, East Sussex and Kent. It has grappled with debt and sustained regulatory and public pressure over pollution performance. Martin Bradley of Macquarie Asset Management said the new shareholder reflected growing confidence in the company’s management and plans, while acknowledging more work remains. The commitment still requires regulatory sign-off, and the company could need further equity if operational progress stalls or regulators restrict the revenue available to fund upgrades.