Around 70 foot of copper piping has been stolen from the sports pavilion on the West Common in Lincoln.
The theft happened on the common off Carholme Road at around 9.45am on March 23.
It is believed men broke in through a small window and ripped the piping off the walls without the water being switched off. Fittings and other piping was also taken.
Lincolnshire Police are keen to find the offenders as part of Operation Brompton.
Anyone with any information or may have spotted someone acting suspiciously around the time should contact Lincolnshire Police on 101, quoting incident number 132 of 23/03/2014, or contact Crimestoppers anonymously on 0800 555 111.
Operation Brompton was set up in 2011 to tackle the rise of metal theft in the county.
The operation aims to reduce metal theft crime; to identify, arrest and prosecute offenders involved; reduce the opportunity to commit the crime by target hardening and disrupting disposal routes; ensure legislative compliance by Scrap Metal Dealers; and increase intelligence.