It's a mega industry, but is it worth it?

Australia's tap water has tested among the best in the world. Why then do we spend over $500 million every year on a liquid that's chemically nearly identical?

Around 1,000 brands of water are on sale in Australia.

More stories from Today Tonight

• Bottled water industry
• Lifting the lid on bottled water
• Wonder water test results

Coca Cola Amatil control 42 per cent of the market, mostly with the top sellers Mount Franklin and Pump Water.

In August last year in Queensland a woman died after contracting a very rare bacteria called mycobacterium abscessus. It got into her lungs, and her doctor thought she may have ingested it from tap water in her home.

Since then her family have boiled their tap water.

More stories from reporter Bryan Seymour

So is there any reason that we should all be doing the same?

Sydney Water Spokesperson Emma Whale says the public's drinking water is subjected to 1.4 million laboratory tests every year.

"We test more than 17,000 samples a year, and we are absolutely committed to making sure what people receive is world's best quality," Whale said.

Today Tonight's latest food and drink stories

"The two things that people maybe do get concerned about are cryptosporidium and giardia. What we do is we actually publish six days a week on our website that our samples are clear of those two bacterium, and we just do that because we're committed to making sure our customers feel entirely comfortable drinking our water."

Two independent laboratories analysed seven unidentified water samples. Six were top-selling bottled waters, while the last sample was just everyday tap water.

In the second laboratory, technicians looked for bacteria in the samples. The tap water we tested had lower levels of sodium, and higher levels of calcium, than the bottled brands.

Other than that, there was virtually no difference in quality. Where they really differ is in price.

Jon Dee, the Managing Director of activist website Do Something is thirsty for an end to bottled water altogether. “It’s $2.50, $3 a litre or more for bottled water, that's twice the price of petrol,” Dee said.

Just over a year ago a batch of Cool Ridge bottled water was found to contain too much chlorine cleaning solution, and the manufacturer recalled the bottles from Queensland and New South Wales shelves voluntarily.

The problem is we don't really know exactly what's going on inside the factories filtering, packaging, and shipping all that water.

"You know the ironic thing is that we're in a lab, and all this (tap) water is being tested. If we wanted to see this testing being done at a bottled water factory, well you can't, because it's all commercial in-confidence,” Dee said.

Ingrid Just from Consumer Watchdog Choice says the main concern about bottled water is waste.

"Consider energy miles, and that is the amount of energy that goes into the production of bottled water, the transportation, the production of the plastic, the cost of getting that water from the source, through the production channels to your front doorstep," Just said.

The tests, again, showed no trace of bacteria or fecal matter in the tap water. Far from being seen as safer, the reason most often given by those who regularly buy and consume bottled water is that it is convenient.

"Of course that's a very valid reason. If, though, you're concerned about the environment, then an alternative is buying one of the reusable bottles, and that way you have the convenience as well," Just suggested.

If the cheaper cost and top quality aren't enough to make you smile, remember tap water has fluoride – while many bottled waters still do not.