Bottled water may be trendy but it's also ecologically stupid. San Francisco's ban on buying it is in place, but could it work here?

I don't subscribe to the view that what happens in California heralds the future, but last week I wondered. On July 1, the mayor of San Francisco introduced a ban on the purchase of plastic water bottles anywhere within the municipal sphere.

Mayor Newsom told voters bottled water is 1,000 times the cost of tap water. Yet millions view bottled water as an aspirational good. It's trendy. In reality it's ecologically stupid. I wonder when retailers will be pressed to phase it out, or take back the bottles for recycling. Not long I hope.

Climate change means that water shortages in places such as California and Spain will have knock-on effects elsewhere.

Recently, floods have dominated UK headlines but access to good water is too easily assumed by rich countries.

The Stockholm International Water Institute repeatedly stresses how water is already reshaping geo-politics and migration. In a world where a third of humanity will suffer water stress by 2025, bottled water is nonsensical.

Introducing the ban, Mayor Newsom stressed how plastic bottles are a waste problem - private trade resulting in public squalor and cost. The Mayor said "more than one billion plastic water bottles end up in California's landfills each year, taking 1,000 years to biodegrade and leaking toxic additives such as phthalates into the ground water". Diverting water into bottles strains ecologies.

Staggering amounts of energy are used in the bottles, bottling and transporting of such heavy goods. A Recycling Institute report showed that 18 million barrels of crude oil equivalent (COE) were consumed in 2005 to replace the two million tonnes of PET bottles that were wasted instead of recycled in the US. A Swiss study found a litre of bottled water used 320ml of COE if the bottle were transported over an extended distance to the consumer (which many are), compared with 0.3ml COE for tap water, which uses one thousandth of the energy that bottles do.

Lifecycle assessments suggest that bottling water imposes a heavier environmental burden. Mass public sourcing is more efficient than individualised supply. Bottle waste has been considered 'normal' for too long - it needs to be exposed. In 2005, 144 billion drink containers were wasted in the US, where consumers paid more than $270bn for the 36 billion gallons of fountain and packaged beverages - roughly what they spent on petrol!

Anyone fancy bringing back a charge for bottles?n

Tim Lang, professor of food policy, City University