Ten regional water authorities were sold together in 1989
Since the Water Act 1973, ten regional water authorities had run water supply and sewerage across England and Wales. The Water Act 1989 broke them up. On 1 September 1989 their water and sewerage work passed to ten government-owned successor companies, each under a holding plc, and their regulatory work went to a new National Rivers Authority. The ten holding companies were then sold together in a single flotation in December 1989, raising £3,594m for the government. The same Act created a Director General of Water Services to regulate prices; Ofwat began as the office supporting that post. Each answer here is the short name of a 1989 plc; the old authority's name also counts. The list is fixed.
Name them all first. Then try the harder part: name them region by region, from the north of England to the south-west.