Keighley householders are being urged to be on their guard against bogus callers.
Yorkshire Water (YW) issued the plea after company clothing was stolen from one of its vans.
It is feared the items could be used by would-be thieves.
A YW spokesman said: “All genuine Yorkshire Water employees carry identification, and on the very rare occasions that we visit customers’ properties, this identification can and should always be verified by calling 0800 1387878.
“While making this call, the customer should close their door on the caller. Genuine callers will have no issue waiting while their credentials are verified.”