Southern Water, one of Britain’s biggest water companies, is drawing up contingency plans to tanker water from Norway to deal with future supply shortages and drought.

Southern, which has 2.7 million customers for drinking water supply in the south-east of England, could import water from Norwegian fjords to provide up to 45m litres a day, and would pay for it from customers’ bills.

Southern is in discussions with the UK private company Extreme Drought Resilience Service (EDRS) to ship the water from Norway when needed. ESRD supplies water in Tetra Pak-style cartons, shipping containers or megalitres delivered by sea tanker, according to Adrian Court, its executive director.

The Environment Agency is understood to be in contact with Norwegian regulators about the plan, which the agency believes reflects the company’s delayed delivery of crucial supply schemes.

The utilities company said using tankers would be a “last-resort contingency measure that would only be used for a short period in the event of an extreme drought emergency”.

Its managing director for water, Tim McMahon, said: “We have a range of other reserve options to call on first, such as temporary desalination plants and water-saving agreements with businesses, to keep Hampshire’s taps running.”

The agency will review Southern’s proposed options – including the plan to use sea tankering from Norway, which was first reported by the Financial Times – through a public consultation and consider their environmental acceptability.

It expects the company to reduce reliance, as part of its drought planning, on taking more water from the River Test in Hampshire, one of the world’s most precious chalk streams and designated as a site of special scientific interest, and the River Itchen special area of conservation.

McMahon said Southern was working to take less water from its chalk streams and to build new reservoirs, such as Havant Thicket in Hampshire.

Water companies are lobbying regulators to allow them to raise bills significantly over the next five years to improve infrastructure. Campaigners argue that consumers have already paid for upgrades that have not been carried out.

Greenpeace UK’s chief scientist, Doug Parr, said: “Decades of neglecting its own infrastructure have left Southern Water having to choose between unappealing options as the climate crisis threatens supplies. Causing permanent damage to local ecosystems by taking more water would be a further foolish concession to the short-termism that got us into this mess.

“Tankering in huge quantities of water from Norway will inevitably be a costly and carbon-intensive alternative to that of doing a better job with the water resources that are available in a rainy country like the UK … Despite the obvious failings of planning, water companies need to start thinking of potable fresh water as a precious and finite resource, and plan to start treating it as such.”

In July, the chief executive of Southern Water received a £183,000 bonus despite submitting a business plan that was criticised by the industry regulator for England and Wales, Ofwat, and attempting to raise water bills more than any other English water company.

Southern is majority owned by the Australian investor Macquarie – which has been criticised for its stewardship of Thames Water – after it received a £1bn cash injection to save it from possible renationalisation in 2021. A further £550m was invested into the company last year.