Water for Tomorrow Act of 2020 This bill provides assistance for water resources development and ecosystem protection and restoration projects in western states. Specifically, among other things, the bill requires the Department of the Interior to provide assistance to water supply projects that would contribute to a safe, adequate water supply for domestic, agricultural, environmental, municipal, or industrial use. Interior must also award grants to help disadvantaged communities with populations of 60,000 or less meet specified drinking water standards or address a significant decline in quantity or quality of drinking water. Further, the bill reauthorizes through FY2026 the rural water supply program, reauthorizes through FY2025 the cooperative watershed management program, permanently reauthorizes certain water management improvement grants, and modifies provisions related to funding for water recycling and reuse projects. Additionally, the bill requires Interior to award grants for habitat restoration projects that improve watershed health to entities with water or power delivery authority. Interior may also enter into agreements to fund aquatic ecosystem restoration and protection projects if they are likely to improve the quality of the environment by improving fish passage. Further, the bill requires the U.S. Fish and Wildlife Service to develop, and update every three years, a plan to sustain the survival of critically important fisheries within western states during future periods of extended drought. The bill also requires Interior to incorporate information from emerging technologies for snowpack measurement when determining water supply allocations and to study the projected impact of climate change on the safety of Bureau of Reclamation dams.