Our guide to caring for and disposing of reusable bags to minimise your environmental impact.

For any bag, the greenest choice is to use it as regularly and for as long as you can – even if the very last usage is as a rubbish bin liner.

When the plastic bag ban kicked in on 1 July, most of us were already packing our groceries in reusable bags. The ban cut one source of plastic pollution – the estimated 750 million single-use bags handed out each year, many of which wound up in our waterways.

So how do the replacements measure up environmentally? That depends on your choice of reusable bags and how often you replace them.

Reusable bags chew up more resources and produce more pollution than single-use plastic bags in manufacturing and transportation. On the flip side, they’re designed to be reused many times. After a certain number of uses, this balance tips in favour of reusable bags, although it may take longer than you’d think.

To determine this tipping point, Danish Ministry of Environment and Food researchers calculated different bags’ environmental impacts compared with single-use plastic versions. Published in 2018, the report examined 13 reusable bag materials and estimated the number of uses:

Here’s how many times you’d need to pack your groceries into five common types of reusable bag to justify making the switch from single-use plastic:

Example: Life Education bag ($3 from The Warehouse) Climate change impact: 53 uses (once a week for 13 months) Full environmental impact: 7101 uses (once a week for 137 years) Disposal options: Landfill, re-purposing (as rags) or try composting (natural fibres are biodegradable but may be unsuitable for small compost bins.)

Example: Trelise Cooper The Eco Bag ($7.99 from New World); Zinc bag ($6 from Countdown) Climate change impact: 24 uses (once a week for six months) Full environmental impact: 871 uses (once a week for 17 years) Disposal options: Landfill or re-purposing.

Example: Bag for Good ($1 from Countdown); New World Bag (99¢ from New World) Climate change impact: 7 uses Full environmental impact: 53 uses (once a week for 13 months) Disposal options: Landfill or Bag for Good returned to Countdown for recycling in Auckland.

Example: Brown paper bag (20¢ from Countdown) Climate change impact: Once Full environmental impact: 44 uses (once a week for 10 months) Disposal options: Kerbside recycling or if contaminated with food, compost or landfill.

Example: Warehouse Stationery bag ($1 from Warehouse Stationery) Climate change impact: 3 uses Full environmental impact: 36 uses (once a week for nine months) Disposal options: Landfill or repurposing.

GUIDE Reusable bag availability and cost based on store surveys in July 2019. NUMBER OF USES based on Danish waste system as no comparable research conducted in New Zealand. Paper bags were used as bin liners, not recycled as the research deemed this had a lower environmental impact. Plastic reusable bags were recycled (currently only available at Countdown for Bag for Good). The study did not assess some types of reusable bag available in New Zealand (such as polyester bags made from recycled plastic bottles). DISPOSAL OPTIONS based on New Zealand supplier information and local recycling and rubbish systems.

Our food safety advice for reusable bags:

You don't need to buy a reusable bag – you can make your own from an old t-shirt.

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I am not virtue signalling (foul term in itself) but have used reusable bags forever and a day, inculcated by parents who were exceptionally austere. What impresses me is that two bags which were promotional chainstore carriers - large and showy and logo emblazoned - are coming up to twenty years old. One is showing vague signs of distress and I am wondering about writing to the UK supermarket chain to complain.......

Many non-food stores where you’ve signed up for discounts/email notifications will automatically email you the sale printout. No paper and you don’t mislay it. Supermarkets could do the same.

The supermarkets have send the specials via emails for years. I can’t remember getting a supermarket flyer as I have a sign on my letterbox that I do not want advertising flyers.

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