Water Affordability, Transparency, Equity, and Reliability Act of 2018 This bill amends the Internal Revenue Code to: (1) establish a Water Affordability, Transparency, Equity, and Reliability Trust Fund; and (2) increase the corporate income tax rate to 24.5% to provide revenues for programs created by this bill. The Environmental Protection Agency (EPA) and the Department of Agriculture must allocate funds from the trust fund to clean water programs, drinking water programs, and water well systems. The bill amends Federal Water Pollution Control Act (commonly known as the Clean Water Act) to authorize the EPA to make grants for providing technical assistance for water and sanitation infrastructure and drinking water systems to rural and small municipalities and tribal governments. The EPA must establish a grant program for repairing, replacing, or upgrading septic tanks and drainage fields. The bill amends the Consolidated Farm and Rural Development Act to make permanent a grant program for household water well systems in rural areas. The bill revises requirements concerning the clean water state revolving fund (SRF) and the drinking water SRF. The bill amends the Safe Drinking Water Act to require the EPA to make grants to local educational agencies for: (1) infrastructure to ensure that drinking water in schools is lead free, and (2) testing drinking water in schools for lead.