Thames Water has recruited a team of detectives after the number of unauthorised connections to their network increased twentyfold.
Thames Water brought in the super-sleuths after the number of cases involving water theft rocketed from 33 in 2011 to 734 in 2017.
Led by a former police detective, the team of investigators are patrolling London and the Thames Valley to find and, if necessary, prosecute.
Last month, cleaning firm Hydro Cleansing pleaded guilty to 18 offences in Croydon and Reading under the Water Industry Act 1991 after illegally connecting standpipes to the network.
They were ordered to pay fines and costs totalling almost £15,000.
The team took another company, Kilgannon Street Care, to court in September after they were seen connecting an unlicensed standpipe to a fire hydrant in Battersea, south west London, and using thousands of litres to clean the streets.
The firm's director admitted 12 offences under the WIA and was ordered to pay more than £5,000 in fines and costs.
Investigator Claire Rumens, formerly of Kent Police CID, added: