Runners will not be able to refill bottles, with water distributed in pouches made from seaweed instead

The capital’s first marathon event pledging to be completely free of “single use” plastic drinks bottles is to take place in north-west London.

The Harrow half marathon on Sunday 16 September will be the first time that London has staged a single use plastic-free running event.

Single use plastic bottles are banned from the course. But runners will be able to rehydrate themselves at water stations along the 13.1 mile course with Ooho, water in biodegradable sachets made from a seaweed-based membrane. Participants can either nip the edge and drink the water or consume the entire capsule.

Runners will not be able to refill their own bottles. Regular water and biodegradable cups will be available but only as a backup in case of exceptionally high demand.

Profile Plastic - what's the problem? Show Hide Why the sudden focus on plastics? Mankind produces roughly its entire body weight in plastics every year. But the vast majority of it is either not recycled, unrecyclable, or doesn't get reused once it's been recycled. Volumes ending up in the natural environment are surging. Plastic can take as much as 500 years to decompose.

What are the implications? Plastic is ubiquitous – and often deadly. It kills sea creatures that eat it but cannot digest it. It gets into the human food chain by contaminating the fish that we eat. It is even in our tap water. There is no science about the long-term impact of humans ingesting plastic.

What is to be done? Taxing plastic bags – or even banning them outright as Kenya has done – has changed consumer and producer behaviour. But what next? Deposit return schemes for plastic bottles work well in several countries. Charging for one-time coffee cups also seems to be on the agenda. But the real solutions may not be top down but ...

... bottom up? Yes. Grassroots movements led the way on plastic bags, and have spawned others such as Refill, which emphasises reusing bottles, and A Plastic Planet, which urges plastic-free aisles in supermarkets. Popular culture remains hugely important: it's just possible that the British series The Blue Planet has changed attitudes overnight.

Photograph: Zakir Chowdhury/Barcroft Images/Barcroft Media

The makers of Ooho, which is biodegradable within six weeks, claim it is a world first and say it aims to curb the devastating effects of plastic on the oceans and the environment.

The move comes as running event companies tackle the issue of plastic wastage at races across the UK. Oohos filled with Lucozade sports drinks and gels will be trialled at the Richmond marathon – also on 16 September – and Tough Mudder in West Sussex on 29 September.

At this year’s London Marathon, compostable cups were trialled for the first time to try to reduce the volume of plastic bottles used and discarded along the track. 90,000 of the recyclable cups were put at three drink stations along the 26.2 mile (42.1km) route.

Last year the Guardian reported that a million plastic bottles are sold worldwide every minute, a large proportion ending up in landfill or in the oceans.

As part of his drive to reduce single use plastic bottles in London, the mayor of London, Sadiq Khan, has committed to delivering up to 20 new water fountains across the city this year. In addition to a new fountain in Carnaby Street in the West End, three more will follow this summer – two in Liverpool Street station and one in Bankside’s Flat Iron Square.