Conservation Reserve Program Improvement and Rural Water Systems Access Act of 2018 This bill amends the Food Security Act of 1985 to reauthorize through FY2023 and modify the Department of Agriculture (USDA) Conservation Reserve Program (CRP). (CRP provides payments to farmers who agree to remove environmentally sensitive land from agricultural production and plant species that will improve environmental health and quality.) The bill authorizes USDA to designate areas of special economic sensitivity as economic priority areas for CRP allocations. These areas include areas with actual and significant declining habitat for specifies of economic significance. A "species of economic significance" is a wildlife specifies: (1) for which CRP is critical to maintaining its habitat, and (2) that the governor of a state verifies provides more than $150 million each year to the economy of the state from hunting and related activities. Additionally, the bill: (1) authorizes cost-share assistance for fencing and water distribution practices, and (2) modifies policies regarding grazing and the mechanical harvesting of vegetative cover on CRP land. The bill also amends the Federal Land Policy and Management Act of 1976 to prohibit the Forest Service from charging rural water districts or associations rental fees for rights-of-way for rural water pipelines that cross National Forest System land.