Abstract
Six mixing models and a number of equations derived from them have been proposed for some possible dissolved solids‐discharge relationships in streams. The equations can be put in a form suitable for statistical analysis by digital computer. In actual application, however, a major problem arises in determining which equation or model is most applicable because the data tend to fit two or more equations equally well. A particular difficulty is encountered in deciding whether a constant component of dissolved solids is present. This decision is most critical when only total dissolved solids or electrical conductivity is used for concentration. An examination of other chemical data, if available, along with knowledge of the stream help decide which model is most suitable. Other problems may arise from factors such as nonrandom trends and variations in the storage volume‐discharge relationship. Under these circumstances, an extension of the equations beyond the range of actual data or inferences about physical or chemical significance of the equations or constant terms should be made with caution.