The test program reported in this paper was undertaken to establish the critical levels of strain, stress, and deflection that exist in flanged joints having dimensions typical of those used with steel pipe lines in potable water-supply systems. Such water systems generally operate at low or moderate pressure levels. The investigation was limited to flanges of the low-hub and plain-ring types attached to the pipe by fillet welds. The design of flanged joints and connections for high-pressure and high-temperature connections has been well explored and reduced to standard procedures. Conditions that exist in water-supply service are generally more favorable than those encountered in similar industrial piping or in pressure-vessel service. Therefore it was hoped that the test program might shed light on possible modifications to the established design approach that prevails in the general field of design.