New Zealand households have saved in their bank accounts over $100 billion, an amount that is twice the amount of savings eight years ago, but financial advisers are saying depositors should think again, Dominion Post reports.

As this developed, mortgage and term deposits crept the closest together than they've been for two years, which implies the banks could use more savings from account holders.

Richard Meadows of Fairfax wrote that many older people who had suffered the results of finance company collapses have been traumatised, and now getting assurance from banks.

But New Zealand Financial Planning's Greg Moyle said letting money sit in the "safety" of banks can make depositors vulnerable to the consequences of inflation.

"It can be a very dangerous thing to do, because it's not going to keep pace with inflation, and effectively you're running down the real return of your capital", he says.

"It's like being on a desert island where it's slowly sinking. You don't notice on a day-by-day basis, and then one day the water's lapping around your waist."

Spicers financial adviser Jeff Matthews told Fairfax saving money in the bank is meant to manage uncertainty about the property or share markets, but inflation is not guaranteed to stay low, and there are other investment vehicles that can offer much stronger returns over a longer period of time.

Mr Matthews foresees that one's buying power will halve within 24 years if money merely stayed in banks even at the current 3 per cent inflation rate.

"If you're 55 years of age, you've got 10 more years of working and 20 years of being retired - you're investing on a 30-year timeframe," said Mr Matthews.