Provincial taxpayers have been doling out money to rent water that flows through Niagara Falls and dams around Ontario — a charge that isn't spelled out on monthly hydro bills.

For decades, the provincial government has been charging for every litre of water flowing through its own power turbines at dams to produce electricity. The tax includes water surging through Niagara Falls.

"It's effectively a water rental," independent energy advisor Tom Adams told CTV's Paul Bliss.

The government charges Ontario Power Generation for the water it uses. Those expenses are passed on from the company to taxpayers.

The hidden fee flowing into mailboxes each month has cost Ontarians around $1.2 billion over the last four years alone, according to Ontario Energy Minister Brad Duguid.

That means taxpayers have been paying an extra unwritten charge of around $5.50 each month for years.

The buried fee wasn't a big deal decades ago when Ontario had the cheapest electricity in North America, said Adams.

But demand for electricity has increased since the ‘80s and ‘90s, and so has the price.

Earlier this month, Premier Dalton McGuinty warned taxpayers that hydro rates would rise as other sources of energy like solar, wind and natural gas were adopted.

Ontario's electricity rates already increased by around $6.12 in May and are expected to jump another 46 per cent over the next five years.

If Ontario were to cancel the fee now, the government would lose about $350 million a year.

But taxpayer Phil Maher maintains that the water tax is an unnecessary fee for citizens who are already drenched in bills.

"We're paying way too much as it is for hydro," he said.

"This is our natural resources; it should be free for us."

With a report from CTV's Paul Bliss