===== mg/L =====

The unit "mg/L" stands for "milligrams per litre" and is commonly used to express the concentration of calcium carbonate (CaCO₃) in water. Here's how it relates to water hardness:

1 mg/L of CaCO<sub>3</sub> means 1 milligram of calcium carbonate in 1 litre of water.
Water hardness is primarily caused by calcium (Ca<sup>2+</sup>) and magnesium (Mg<sup>2+</sup>) ions in water. To quantify hardness, water testing often measures the concentration of these ions and expresses it as an equivalent amount of calcium carbonate in mg/L.

**Converting mg/L to other hardness units:**
  * Degrees of Hardness (°dH): Water hardness can also be expressed in degrees German hardness. 1 °dH is approximately equal to 17.8 mg/L of CaCO₃.
  * Parts Per Million ([[:snippets:ppm|ppm]]): For water hardness, mg/L is numerically equivalent to [[:snippets:ppm|ppm]]. So, 1 mg/L is the same as 1 [[:snippets:ppm|ppm]].

Example:
If water hardness is measured as 200 mg/L CaCO<sub>3</sub>, it means the concentration of calcium carbonate is 200 milligrams per liter of water. This value indicates relatively hard water, as higher concentrations of CaCO₃ result in increased hardness.