Even with the presidential race tightening, one issue in a drought-parched region of California has remained constant — water and the lack of it. “Water right now is the number one issue for us in the Central Valley,” said Republican Rep. David Valadao, whose congressional district includes some of the state’s largest agricultural production but has been hit hard by the 5-year-old drought.The drought impact goes beyond agriculture in the San Joaquin Valley. Water tables in rural communities in parts of Fresno, Tulare, Kings and Kern counties have dropped and residential wells are running dry.