Combined, the three west African countries produce around 28,000 tonnes of plastic waste from packaged drinking water per year, the researchers found. "This has significant environmental implications," said Nicola Wardrop from the University of Southampton, UK.

As waste collection and disposal facilities are limited, much of this plastic ends up back in the environment. In Nigeria alone, nearly 5000 tonnes of plastic water sachets are dumped in unauthorised heaps each year, the study suggests. In Ghana and Liberia, some plastic waste is burned – a concern for both the environment and public health.

Ghana is the biggest consumer of packaged water, with 11.3 million litres bought each day, the team estimated. To cut such consumption, governments could invest in drinking-water supply to households. This would ensure safe water provision and the best outlook for the environment, but Wardrop and colleagues stress that this can’t be implemented fast enough to deal with the waste. Instead, they believe, the focus should be on improving waste collection routes, as they will immediately reduce the impact of plastics on the environment.

"The results really highlight the joint impact of sachet consumption and lack of recycling services," said Wardrop. 

Currently, demand for waste disposal far exceeds supply, with 63% of Nigerian households, 57% of Liberian households and 20% of those in Ghana lacking formal waste-disposal facilities, let alone a means of recycling the waste. Grass-roots initiatives are tackling some of the shortfalls. With the help of these and private companies, governments could better tackle plastic pollution.

At nearly 150 litres, the amount of packaged water consumed per head each year in Ghana is comparable with levels in the US, where there is access to ample safe water on tap. Levels in Liberia (31 litres) are similar to those in the UK.

Wardrop and colleagues reported their findings in Environmental Research Letters (ERL).