The NHS in England wasted more than £40 million last year by paying too much for its energy and water, research revealed.
Money spent on excessive utility bills could have paid the salaries of more than 1,350 extra nurses, the TaxPayers' Alliance (TPA) said.
The NHS in England spent more than £630 million on energy and £80 million on water 2012-13.
But if NHS sites had paid the average rate, this could have saved more than £41.4 million.
The TPA, which based its analysis on official NHS statistics, said a number of hospitals could have saved more than £1 million each just by getting a better deal for their energy costs.
It has now called for a "war on waste" in the NHS.
Matthew Sinclair, chief executive of the TPA, said: "People pay a lot of money to support the NHS in their taxes and they expect to see every penny possible spent on front-line care, not wasted overpaying for basics like energy and water.
"This is just one way for the NHS to save millions and ease the pressure on its finances created by years of runaway growth in costs."
If sites which overpaid had instead paid the average rate, they would have saved at least £37.8 million on the £630 million total bill.
And if sites that overpaid for water had paid average rates, this would have saved £3.6 million.
The research highlighted four of the most wasteful hospitals - Peterborough City Hospital, Queen Elizabeth Hospital in Birmingham, Eastbourne District General Hospital and Royal Devon and Exeter Hospital - which could each have save more than £1 million had they paid average rates for energy.
A further 19 could have saved over £500,000; 40 sites could have saved more than £250,000; and 74 sites could have saved more than £100,000 in 2012-13.
By paying average rates for water, six NHS sites could have saved more than£100,000.
The study also highlighted trusts that had saved taxpayers money.
Royal Liverpool and Broadgreen University Hospitals NHS Trust's Royal Liverpool Hospital, a site with among the highest energy consumption in England, would have spent £4.6 million more on energy had it paid the average rate.
The TPA said many trusts could make significant savings by emulating others that spent their money more wisely.
Mr Sinclair said: "Before trusts complain about pressure on their finances now that the bumper increases in funding have dried up, they should take these kinds of opportunities to secure better value for money.
"They need to shop around for a better deal. It is time for a war on waste in the NHS."