Glyphosate [N-(phosphonomethyl) glycine] phytotoxicity was assessed with different sources of natural water carriers to establish to what extent ions in these carriers antagonize glyphosate activity. Glyphosate phytotoxicity with the most antagonistic carrier was 72% less than with deionized water. Antagonistic cations were calcium, sodium and magnesium. Antagonistic anions were bicarbonate, chloride and sulphate. Combinations of ionic factors such as total hardness, total dissolved solids and electrical conductivity were excellent indicators of the antagonistic capability of carriers. Multiple regression analysis indicated that calcium and magnesium and the anion bicarbonate were the most antagonistic ions in combination.