A Stiff diagram turns a sample into a polygon — its width shows how mineralised the water is, and its shape is a fingerprint of water type that you can compare at a glance or plot on a map.
How it's built
Cations are plotted to the left of a central zero axis and anions to the right, each on its own horizontal line in meq/L. Connecting the points makes a closed shape. Hydrochart uses the standard three-row layout: Na+K, Ca and Mg on the left; Cl, HCO₃ and SO₄ on the right.
What to read
- Width = concentration. A wide polygon is a more mineralised (higher-TDS) water; a narrow one is fresher. Because the axis is meq/L, the horizontal spread is directly comparable between samples.
- Shape = type. A polygon that bulges at the top (Na and Cl) is a Na–Cl water; one that bulges in the Ca and HCO₃ rows is a fresh carbonate water. The same water type keeps the same silhouette regardless of size.
- Asymmetry = dominance. A shape that leans strongly left or right shows whether cations or anions carry the ionic load.
Watch for
Stiff shapes are qualitative. They're excellent for pattern-spotting and communication, but for precise classification or charge-balance checking, pair them with a Piper plot and Hydrochart's QA flag. Very dilute samples produce tiny polygons that can be hard to compare — switching to Schoeller (log scale) helps there.