Ofwat is the regulatory body for the water sector. They monitor and control the privatised water and sewage industry in England and Wales.
The Water Services Regulation Authority is an independent regulator that was first founded in 1988. They operate in a similar way to other regulatory bodies you may have heard of, like Ofsted, Ofcom, and Ofgem. They are set up as a part of the government's strategic priorities to create better value for business utilities.
Ofwat is a non-ministerial department. This means that it is a department in its own right but does not have a minister that governs it.
Specifically, they are an economic regulator. It is responsible for monitoring prices, setting limits, protecting consumers, and emphasising the importance of investment in the water industry.