Water Affordability, Transparency, Equity, and Reliability Act of 2021 This bill provides funding for several programs related to controlling water pollution or protecting drinking water, revises requirements concerning the clean water state revolving fund (SRF) and the drinking water SRF, and creates or reauthorizes several grant programs for water infrastructure. For example, the Environmental Protection Agency must establish a grant program for repairing, replacing, or upgrading septic tanks and drainage fields. In addition, the bill makes permanent a grant program for household water well systems in rural areas. It also increases the amount of appropriations for grant programs, including a program that awards grants to prevent lead from contaminating drinking water fountains in schools and day care facilities.