There is clear, blue water between the two sides in the battle for Severn Trent . If the consortium considering a firm offer for the UK water utility wants to bridge the divide, it will have to win the debate over the company's debt.

Regulated utilities like Severn Trent ought to be easy to value. Ofwat, the UK regulator, publishes regularly its calculations of UK water companies' regulatory capital value, or RCV. This takes into account each company's initial worth, their capital spending and debt, all adjusted for inflation. Severn Trent's RCV at the end of March was £7.4bn ($11.1bn).