Imperial Beach wants more residents to start using rain barrels. That’s the goal behind a new set of guidelines adopted by the city last week, which officials hope will ultimately help shore up the city’s aging infrastructure against rising sea levels. Rain barrels are tanks that collect and store rainwater for future use. They can help users conserve drinking water and save money on irrigation. They also have the added advantage of reducing the amount of rainfall that flows into the city’s stormwater collection system.