Thames Water faces a multi-million pound bill for the chaos caused by a burst water main on the Thameslink route in central London since last Friday (23 January).
The utility said the incident was caused by a blocked pipe, and blamed “a lack of maintenance”.
Network Rail engineers had to carry out emergency pumping following the incident, but the flooding returned yesterday (28 January) and the rail operator again had to close the line between St Pancras and Farringdon in the evening.
Thames Water said it spent the night working with Network Rail to clear their drains in the tunnel as there were concerns as to why water from the original burst water pipe had not drained away.
The utility’s director Bob Collington said: “The water in the tunnel cleared as soon as we cleaned out Network Rail’s surface drainage system last night. The pipe was full of silt and debris, and a grill which would have allowed the water to drain away was blocked solid. Basically, the water had nowhere to go.
“We believe this problem was first identified as far back as 2007, and the problems with water on the track have been caused by a lack of maintenance on their part.”
Thames Water said it had repaired the original damage to the 400mm-diameter pipe, in the bus lane of Farringdon Road at the junction of Vine Street Bridge, on Sunday morning. When the flooding returned, it sent in specialist teams to carry out further investigations, which uncovered the blocked pipe and grill.
Over 1,000 trains have been cancelled since the main burst on Friday with a further 133 hours of combined delays to those trains which have been running.
Phil Verster, route managing director, Network Rail, said: “We continue to work with Thames Water but the overwhelming extent of the continued flooding made it unsafe to run normal through services between London St Pancras and London Blackfriars since Sunday.
“We have several high output pumps operating but the service is still hugely delayed. We expect Thames water to reimburse passengers, train operators and Network Rail for the significant consequences of these water leaks.”