More than 50,000 residents of Santa Cruz County are reliant on a single water source: the dwindling Mid-County Groundwater Basin, which the state deemed “critically overdrafted” nearly a decade ago. Now local agencies are embarking on efforts to boost the ability of the basin to capture more rain during the wet months along with an ambitious plan to replenish the basin’s drinking water supply with recycled wastewater. A number of agencies — including Soquel Creek Water District, the City of Santa Cruz Water Department, the Central Water District — and several thousand private well owners share the underground basin, a reserve made up of a group of linked aquifers, in an area that encompasses the Eastside of Santa Cruz, Live Oak, Soquel, Aptos and Capitola.