And their verdict? It really doesn't look much different to a regular house at all. There are all the usual appliances, constant electricity, fresh running water and a perfectly stylish bathroom.

The major difference is simply that the energy and water bills are minuscule - below $300 a year for the family of four living there - and the sense of satisfaction for its residents is immense.

"I think people are often overwhelmed by the idea of going off-grid but when they see how simple my house is, they all start thinking, 'Yes! I can do this!'," says the house's owner, sustainability champion Michael Mobbs.

"You can't get more straightforward than the energy coming from the sun and the water coming from the sky. You don't have to be technically gifted, or speak English or even be an adult to do something like this. If I and my six-year-old son and 10-year-old daughter could do it back in 1996, then anyone can."

What does 'off-grid' actually mean?

Going off-grid basically involves disconnecting from mains water, sewerage and electricity, and people usually choose to do one of those things, two or all three.

Often they opt to do the work as part of a renovation or on a new build, when things like rainwater tanks, new plumbing, solar panels and batteries can be easily added. But it's also quite possible to retrofit a home to make it more self-sufficient.

In terms of electricity, solar energy is the most practical and affordable option, and prices of solar systems have plummeted in the last 20 years. Today, says Mr Mobbs, a solar system for a three-bedroom house will cost about $2000. To then disconnect the house, there's the added cost of about $17,000 for batteries - in total the size of a kitchen fridge - to store the energy produced during sunny days to use on cloudy days or night time.

Rainwater is a marvellous source for drinking water and for this you need to install rainwater tanks, and to upgrade taps and shower fittings to make sure they're more efficient. A plumber will be able to advise on what system, costing about $11,000, might best suit your house.

"Grey" water - the water left over from showers, baths, basins and washing clothes - can then be treated and used for functions like watering the garden or flushing toilets.

The sewage question for those wanting to go completely off-grid is perhaps the trickiest. Some local councils are cautious about allowing people to treat their own sewage but, with permission, there are a number of options, like composting toilets and worm farms. A complete sewage recycling system could cost another $11,000.

Mr Mobbs, who now runs short courses teaching people how to go off-grid, says he's always amazed that people can be so cautious about off-grid living, especially when they profess to be environmentally-conscious and keen to save on water and power bills.

"People are often so curious about the latest iPhone or product but when it comes to how we drink, wash and excrete, we don't seem to be curious at all," he says. "We think it's something we can never get to grips with.

"But we can, it can pay for itself within 10 years, and it's wonderful to feel that you're doing your bit for the environment, as well as protecting yourself against future price rises."

Case study: Off-the-grid in Newtown

When communications consultant Kylie Ahern renovated her Newtown terrace, she decided to turn it into the area's first off-grid house.

As well as selecting the usual fixtures and finishes, she also bought a solar panel system with battery storage capacity, an 8000-litre rainwater storage tank to be installed underground in the backyard for drinking water, LED lighting, and plumbing for wastewater treatment.

Good insulation, draught-proofing, a skylight and windows in the walls to maximise sunlight and new, high-efficiency appliances completed her shopping list.

Newtown resident Kylie Ahern is renovating her Newtown house to take it off the grid. Photo: Pat Stevens

Now halfway through, Ms Ahern, 47, who runs her own company Stem Matters, says she's learnt some valuable lessons. "The going off-grid part is easy compared to the renovation!" she says. "It's the renovation that's become so problematic.

"The sustainability aspects of the house have been the cheapest, and simplest, aspects, and it's going to be wonderful to be able to contribute so directly to protecting our waterways by keeping as much stormwater as possible on site. I'm also looking forward to having very small, or non-existent, power and water bills."

Ms Ahern aims to finish her renovation into what will be an almost completely new house, with its own solar power, rainwater, water recycling and composting system in July 2018.

How much does it cost to go off the grid?

• Solar panels and wiring - $2000
• Battery storage - $17,000
• Rainwater collection and storage - $11,000
• Sewage recycling system - $11,000
• TOTAL - $41,000