United States Environmental Protection Agency (USEPA) has regulated drinking water since the 1974 Safe Drinking Water Act (SDWA). Congress directed it to achieve three conflicting goals: (i) establish stringent nationwide standards, (ii) ensure that these standards are both technologically and economically feasible, and (iii) accommodate significant differences in cost among water systems of different sizes with different water sources. USEPA chose to emphasize goal (i) at the expense of (ii) and (iii). In 1986, Congress intensified its preference for (i), was silent concerning goal (ii), and criticized USEPA for failing to achieve goal (iii). In lieu of economic feasibility, the Agency substituted “affordability,” defined as expenditures up to 2.5 % of national median household income irrespective of the benefits. This imposed deadweight losses, and substantial inequities on rural areas, low-income communities, and low-income households generally. In 1996, Congress directed USEPA to use benefit-cost analysis positively and normatively. Regulations issued since 1996 do not appear to comply, however. A review of post-1996 drinking water standards indicates that most were certified by USEPA as having benefits that justified costs, but these determinations were unsupported by the Agency’s own regulatory impact analyses. This article proposes that USEPA define by regulation that “economic feasibility” means marginal benefits exceed marginal costs for the smallest water system subject to SDWA, and that all future drinking water standards must be economically feasible. Economic efficiency would be greatly enhanced and the pervasive inequities of “affordability” greatly diminished. Unlike “affordability,” this definition is objective and compatible with lay intuition about the meaning of key regulatory terms.