Ofwat's decision to reject Thames Waters' bid to increase prices by 8% is final, but Thames Water could appeal to the Competition Commission.
The company said: "We will review the decision carefully before deciding on our next steps."
More top news
Heavy thundery rain for parts of Northern Ireland and Scotland
Four men are being interrogated in Spain's National Court over the vehicle attacks that killed 15 people and wounded more than 120 others.
In the position paper the Government sets out plans to ensure that cross-border legal disputes are dealt with in a "fair way" post-Brexit.