To amend the Food Security Act of 1985 with respect to nutrient and soil health management and source water protection, and for other purposes.

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.