If you haven’t been taking seriously the drought affecting Southern New Hampshire, state environmental officials hope to change that. The Department of Environmental Services is expected to issue a warning about the federally declared drought in the state’s three most populous counties — Rockingham, Hillsborough and Strafford. “If they are on public water, and their utility has implemented any water restrictions or bans, they should become knowledgeable about those bans and follow them,” said John Martin, DES spokesman. Even if your city or town hasn’t issued a formal ban, the DES is recommending that residents in the three counties refrain from watering grass, and that they water flower or vegetable gardens by hand, not sprinklers. More than 50 cities and towns, mostly in the southern tier, have already imposed water-use restrictions or bans on outdoor use in certain neighborhoods.