The city will be making its water treatment plant on Cove Street more energy-efficient through a $45,000 state grant, according to Mayor Scott D. Galvin. The Department of Energy Resources’ Green Division is providing the funding through a program that supports clean-energy projects at drinking water and waste-water facilities. The Woburn project involves replacing outside lights at the plant with energy-efficient models. The city is required to fund 10 percent of the cost, with the state grant covering the rest. Woburn was eligible to seek the funds because it is a state-designated Green Community, a status provided to cities and towns that undertake certain programs to become more energy-efficient and to expand their use of renewable energy.