Ofwat has launched a new consultation on a recent change of ownership for Southern Water resulting from the recent acquisition by a new investor of a substantial minority stake in a holding company of the utility.

To assess the new owner, Ofwat has reviewed information it has received from Southern Water and the new investor itself, funds managed by Madrid-registered Asterion Industrial Partners SGEIC, S.A. which is regulated by the Spanish financial regulatory agency, CNMV3

Asterion is an independent European infrastructure investment manager established in 2018 - Asterion Industrial Infra Fund III, FCR is the legal holder of the minority investment.

The Fund has a diverse investor base that includes pension funds, endowments, insurance companies, asset managers, family offices and sovereign wealth funds (with no single majority investor). In respect of the Fund, the management, representation and powers of control have been vested in Asterion, and all professionals responsible for sourcing, analysing, approving, executing and monitoring its investments operate through Asterion. Accordingly, Asterion is the entity that exercises effective control over the Fund, without being owner of the Fund.

Although Southern Water is the Fund’s first direct investment in an appointed water and sewerage undertaker in England and Wales, Asterion’s senior leadership brings direct UK sector expertise with several team members previously holding key roles at South Staffordshire Plc (including positions of CEO and Chairman).

With the exception of its interest in Southern Water, Asterion has no investment or other interest in any other UK water business and has confirmed it is not aware of any actual or perceived conflicts of interests in respect to the investment in the Southern Water group.

Ofwat says:

"Asterion has set out its position as a long-term engaged infrastructure investor, able to provide strategic support, challenge and sector expertise to support delivery of Southern Water’s AMP8 capital programme and regulatory obligations, alongside the company's turnaround."

The Fund's investors are represented by an advisory board with mainly information rights, but members do not sit on the Asterion board or investment committee, and its functions do not extend to any day-to-day activities over portfolio companies.

Under the current corporate and ownership structure, Macquarie Super Core Infrastructure Fund SCSp, Macquarie Asset Management Europe Sarl (MAM) and Sandstone Water Holdings Ltd, have already been identified as Ultimate Controllers. Ofwat considers that the role of each as Ultimate Controller is unaffected by the change in ownership.

Ofwat has concluded that Asterion, with effective control over the Fund and a right to nominate for appointment representation on the board of Southern Water, is identified as “a person able to exert material influence over Southern Water.” Accordingly, Asterion is also identified as an Ultimate Controller.

An “Ultimate Controller” is defined as any person which, whether alone or jointly and whether directly or indirectly, is, in the reasonable opinion of Ofwat, in a position to control or materially influence the policy or affairs of the water company, or of any holding company of the water company.

In July 2025, Southern Water announced it had secured a further equity package of up to £1.2 billion from its investors (led by funds managed by MAM) to support its AMP8 investment programme.

At the same time, as part of the equity injection process and wider group restructure, MAM acquired, via a newly established investment company Sandstone Bidco Limited (SBL), the issued share capital of Greensands Junior Finance Limited and Southern Water Greensands) Financing plc from Greensands (UK) Limited, an intermediate holding company.

In March 2026, Southern Water announced it had received, in line with commitments, new equity totalling £900 million from SBL, via funds managed by MAM, and confirmed SBL's intention to provide up to a further £300 million of binding equity commitments and to support the company to further reduce its leverage.

In June 2026, Southern Water announced that it had secured the additional £300 million commitment, with the majority to be funded by new investor Asterion (through subscriptions for new shares) and the balance by MAM managed funds.

In July 2026 the European Commission cleared the acquisition, concluding no competition concerns, and the transaction completed in August 2026 with Asterion taking a 20% minority shareholding in the group. The equity commitment to Southern Water is binding with no conditionality and is expected to be drawn down in full on or around 31 March 2027.

Via the consultation Ofwat is now seeking responses to the following questions:

1. Do you have any views on, or our assessment of, the incoming owner?
2. Do you agree with our identification of the Ultimate Controllers?
3. Do you have any further comments on the assessment set out in this document?

As part of its duty to secure that water companies properly carry out their functions, Ofwat says it aims to ensure that any Ultimate Controller of a water company:

• has the capability, operational and financial, to run such an essential public service as a water utility both understands and is committed to these responsibilities
• in Ofwat's view meets the licence definition of Ultimate Controller.

Closing date for the consultation is 30 October 2026. Click here to read the consultation document. To submit a response to the consultation, make any comments or ask any questions email This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Postal address to submit a response is:

Financial Resilience Change of Control consultation response, Ofwat, Centre City Tower, 7 Hill Street, Birmingham, B5 4UA.