Government departments in Northern Ireland have failed to spend more than £400m from their budgets in the last year.
Ian Pearson said the money would be spent on public services
It is the third year in a row there has been an underspend, with £365m left in the government kitty after the previous 12 months.
Finance minister Ian Pearson said the underspend was not a problem but pledged the government's financial planning would be improved.
But with plans to introduce water charges well advanced, there has been criticism of the way the government calculates its future spending.
The government insists that water charges and job cuts are essential to fund improvements to the service but trade unionists have questioned the plans.
Jim Walsh from the public service union NIPSA claimed a third of all rates already went to the water service.
He said: "All this talk about water charges at a time of a significant underspend - I think it is unfortunate that they won't admit the problems."
The shift from devolution to direct rule is one of the reasons put forward to explain why the flow of money has been disrupted.
Mr Pearson said the problem was recognised when the executive set the last budget.
"We do need to get better at our financial planning as a government but this isn't money lost.
"The key message is this is money that is being spent now, in our schools and hospitals and on our public services."