Properties in the Meikle Inch Lane area of Bathgate are understood to have been affected by flooding, while water supplies in parts of Bathgate, Blackburn and Livingston were disrupted.
It is the second time the water main has burst in a week.
Scottish Water said engineers have made progress restoring supplies.
On Wednesday morning, the water main burst around 8:20am with witnesses reporting “rivers of water” at the peak of the incident. It took seven hours before Leyland Road and Meikle Inch Lane reopened, with the flooding affecting 17 properties. Five nursery schools in the area were also closed for children in the afternoon.
Yesterday, resident Mark Snedden said the renewed flooding had caused panic. He said: “We ran out of the house to move our cars to safety based on how high the water had got on Wednesday. We then rushed to some of our neighbours’ homes, neighbours that had been flooded, to let them know that the water had returned because they were actually walking in their flood-damaged homes.”
Scottish Water apologised “unreservedly” for the inconvenience caused.
The firm said: “We have teams on site in the Meikle Inch Lane area that have isolated the burst and introduced backfeeds into our network. This has enabled us to restore normal supplies to the majority of customers who were affected. Water tankers are also available if needed to support the network.
“We have staff on site to help support affected customers and we are liaising with other agencies such as West Lothian Council and the Scottish Fire and Rescue Service. Incident teams have been running through the night with senior management continuing to be involved in managing the repair and recovery effort.
“Our main priority is to do everything that we can to help customers affected by flooding and loss of water supply – for some, the second time this week – and to provide the necessary support they require.
“We will investigate whether we can isolate this section of main whilst maintaining supplies to ensure that there is no repeat of this burst.”