It is the primary duty of the county attorney in Harris County or his assistants to represent the state, Harris County, and the officials of Harris County in all civil matters pending before the courts of Harris County and any other courts in which the state, the county, or the officials of the county have matters pending. The county attorney shall represent the Harris County Flood Control District and perform the other duties imposed by this section without any additional fee, compensation, or perquisite other than that paid by Harris County out of its officers’ salary fund.