A Schoeller diagram plots every major ion on one semi-log chart, so you can overlay many samples and read water type, dominant ions and relatedness from the shape and spacing of the lines.
How to read it
The six major ions sit at fixed positions across the x-axis; concentration in meq/L runs up the y-axis on a logarithmic scale. Each sample is a line connecting its values. The log scale is the whole point: it lets a very dilute and a very concentrated water appear on the same plot, and it makes proportional relationships show up as shape.
What the lines tell you
- Parallel lines = same water type. On a log axis, multiplying every ion by the same factor just shifts a line up or down without changing its shape. So parallel lines are chemically alike — related by dilution, concentration or mixing.
- Vertical position = concentration. Higher lines are more mineralised waters.
- Peaks and troughs = dominant ions. The shape immediately shows which cations and anions dominate — a high Cl point with a high Na+K point flags a Na–Cl water.
- Crossovers = different processes. Lines that cross or change slope between ions signal genuinely different chemistries, not just different strengths.
Watch for
With many samples the plot gets crowded; group and colour rather than showing everything at once. And because the axis is logarithmic, small vertical differences can represent large absolute ones — always keep the meq/L scale in mind when judging magnitude.