If it fills in less than a minute, the shower flow is faster than necessary.
Just adding a flow restrictor disc or replacing the showerhead with a more efficient one would save about $400 a year for households having three showers a day, he said.
"It doesn't need to cost the earth. We reckon it's easy to [cut bills by] 10 per cent," Hoerning said.
"It depends a bit on how committed you are already and how much more committed you want to be.
"There are things that can easily add up to several hundred dollars, if not $1000, in savings a year. Electricity prices might be going up but you've got control over how much you use."
Robert Adamson, of Right House, said most people were oblivious to how much power they used and what they could save.
"When we put solar on someone's house and they become aware of their usage, they often realise they're able to save a lot just by turning things off. We're all very busy and just forget."
He said people could usually save 10-15 per cent by shopping around for the cheapest supplier via websites such as Whatsmynumber.co.nz, and then being sensible about their power use. "Some people are savvy but the bulk of people aren't."
Leigh Featherstone, director of Homestar, says the time at which you use your appliances can make a difference to your monthly bill.
"Energy costs more at times of the day when there's high demand, such as early evening when families are home from school and work."
Timers could be used to set the washing to start during the day and spa pools could be set to heat only during the cheapest hours. He said New Zealanders were becoming more aware of the importance of insulation and sunlight.