Just one in three customers think South West Water delivers value for money – by far the worst rate in the country.
A survey for the Consumer Council for Water revealed that only 35% of people thought the water company, which has historically had the highest bills in the UK, gave value for money.
The rating for South West Water was less than half of the national average of 72%. The national table was led by Northumbrian Water with 83%.
Overall, 86% of people in the region were satisfied with the service they received, just under the national average of 92%.
The council said South West Water had the "hardest job to do" to improve its value for money rating but said the result was "unsurprising" given the price that consumers had paid for cleaning up the region's beaches.
Tony Smith, chief executive of the consumer council, said: "Customers' views reflect the continuing price increases and water companies' lack of communication about what they are doing with the extra money they are getting from customers.
"We will be pushing water companies, particularly the poor performers, to improve their communication with their customers and show an improved trend on customer satisfaction with value for money.
"We will also be pressing for water regulation to incentivise water companies to improve this vital measure of success for the industry."
The council said customer satisfaction regarding value for money for water and sewerage was broadly in line with the energy sector where bills were much higher.
It has published the full report on its website, allowing water customers to compare the results for their company across the industry.
A spokesman for South West Water said it was "pleased" with the overall satisfaction figure of 86% and was "working hard to build on that". It also welcomed that the consumer council recognised the South West's "special circumstances" having just 3% of the population but a third of the country's beaches.
Over the last 20 years, £2 billion has been spent to ensure 146 bathing waters meet EU cleanliness standards.
Customer relations director Monica Read said: "In many aspects of this survey we do well, but we do understand the sense of unfairness many people feel that a small population has to pay for such a major coastal clean-up.
"We have worked hard with others to make this case at the highest levels and thanks to those efforts we are currently putting in place plans to pass on the £50 for every household from the Government from next year.
"This legislation was passed in recognition of the investment the region has made in its bathing waters, which are enjoyed by people from all around the UK and beyond."