Pensioners are being warned to check the identity of callers at their home.
It follows a spate of thefts from bogus officials in Fylde, Preston and Euxton, near Chorley.
Police say they were targeted by two conmen on Saturday with the men, aged 30 to 40, claiming to be water officials.
They then gained entry to the houses before stealing cash and credit cards from the properties.
The men were described as white with beards and with Irish accents.
One was tall and wore a brown suit, and the other was smaller, stocky and was wearing a green army jacket and cap.
A black car was spotted near the scene of some of the thefts.
Police are appealing for anyone who may have information about the incidents, or the car, to contact them.
Call Crimestoppers on 0800 555 111.
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