The Ofwat board is divided over whether to approve a rescue deal proposed by Thames Water's creditors.
The lack of consensus among the eight board members follows a deal floated last month by senior creditors to stabilize the utility.
The ongoing split increases the risk that Thames Water could collapse into special administration, threatening the future of the UK's largest water company.
Will Thames Water's rescue deal truly fix its environmental crisis, or just reward creditors?
Are customers facing higher bills and worse service, while Thames Water's shareholders walk away clean?
With a new regulator planned, is Ofwat's current struggle over Thames Water already obsolete?
Could Thames Water's collapse spark a fundamental overhaul of the entire privatized UK water industry?
Beyond the £10 billion debt, what is the true long-term cost of Thames Water's crisis for UK taxpayers?
If special administration isn't to be feared, why is the government so keen to avoid it for Thames Water?