Thames Water, Southern Water, Affinity Water and Hafren Dyfrdwy have come bottom of the industry watchdog’s annual performance report.
Ofwat singled out the companies and urged them to “deliver a real change in performance”, while praising the work of Northumbrian Water, Wessex Water, Bristol Water and South Staffordshire Water.
The regulator found that the sector overall is making good progress on areas including leakage targets, reducing supply problems, and improving customer services.
But officials found that pollution remains a significant problem that the sector must do more to address.
Ofwat highlighted South West Water’s “extremely poor performance” in missing its pollution targets for the past five years, and Southern Water for being rated one star by the Environment Agency since 2015.
Water consumption levels were also poor, with just three companies meeting their targets on encouraging households to reduce their usage, it added.
Customer satisfaction has generally improved, the report said, with Ofwat pointing out that those with good performance stand to make significant outperformance fees.
Poorer suppliers face penalties of up to £20 million without improvements in customer service.
One area of focus for the regulator has been reducing supply interruptions to homes, and Ofwat said this has improved, with a 36% reduction over the past seven years.
Chief executive Rachel Fletcher said: “It is encouraging that some companies are making good progress by listening to customers and improving the service they provide.
“But others are falling short of expectations and still have much ground to cover. They must act with urgency and real commitment, to meet the standards people deserve.”
She added: “Environmental performance is still not good enough. Minimising water companies’ impact on the natural world and leaving the environment in a better state for future generations will only happen if the environment is given greater attention.
“New targets for the coming year will start to bite if faster progress is not made in this area.”