Chessington World of Adventures is closed all day on Friday because of a water shortage caused by a burst main.
The theme park apologised for the "frustrating" news in a statement, but said it had made the decision for "the health and safety" of guests.
The burst main has been affecting homes and businesses near the park, in Surrey, since 03:00 BST.
Tickets booked for Friday can be used at Thorpe Park and Legoland, the park added.
The park has confirmed it will reopen on Saturday with the water supply restored, but urged people to still check its website in the morning for the most up-to-date information.
Among the visitors who were turned away was Emma Ashford, 25, who had travelled from her home in Par, Cornwall, to the theme park for her daughter's fifth birthday.
Ms Ashford said: "My daughter was upset at first because she had been telling everyone at school that she was going to Chessington. The staff were giving out bottled water to people waiting, making sure they were hydrated.
"After being told the park wouldn't be opening, we ended up travelling to Windsor instead."
1/3 Adventurers, following the closure of our Theme Park and Zoo today, we’re pleased now to be able to confirm that we will be open tomorrow and it’ll business as usual, as we’re confident Thames Water has restored our water supply.— Chessington Resort (@CWOA) July 27, 2018
Chessington said disruption was "tough" on businesses in the area.
It added: "Network suppliers, such as utilities, need to acknowledge the consequences, both financial and reputational, of such major disruption."
The park said bottled water was being used to help meet some animals' needs.
Thames Water said it was "really sorry to those who have been affected by a burst water main in Chessington".
It was working to "get everything back to normal as quickly as possible" by re-routing the network, the firm added.