Progress in Earth and Planetary Science

Table 3 Water hardness classification

From: Coastal sand dune ecosystem services in metropolitan suburbs: effects on the sake brewery environment induced by changing social conditions

Hardness classification	USA hardness (ppm)
Soft water	0–60 less than^a
Medium hard water	60–120 less than^a
Hard water	120–180 less than^a
Very hard water	180 or more^a

^aWorld Health Organization (2011)

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