Collaborative Water and Soil Enhancement Act of 2018 This bill amends the Food Security Act of 1985 to establish requirements for Department of Agriculture (USDA) conservation programs regarding: (1) nutrient and soil health management, and (2) source water protection. In carrying out the Conservation Stewardship Program and the Environmental Quality Incentives Program, USDA must: enroll at least five million acres annually in watersheds where nutrient delivery to hypoxic (low oxygen) zones is highest; encourage water quality or water quantity practices that protect source waters for drinking water (including protecting against public health threats) while also benefitting agricultural producers; collaborate with community water systems and state technical committees to identify local priority areas for the protection of source waters for drinking water; offer increased incentives and higher cost-share rates for water quality or water quantity practices that result in benefits that primarily occur outside of the land on which the practices are implemented; and reserve at least 10% of the funds or acres available for the programs to target the most effective practices for improving the quality or quantity of source water. USDA must also provide a streamlined certification process for third-party technical service providers that have certain certifications from the American Society of Agronomy.