Rare literary noun referring to a fluid, changeable, or wanton nature. Modern Japanese more often uses 流動性 for 'fluidity' and みだら or ふしだら for 'wantonness'.
In old texts, one can find expressions warning against a woman's wantonness.
水性 can refer to a fluid, unsettled nature like water.
Compound of 水 (water) and 性 (nature, character), literally 'water-like nature'. The exact historical derivation is uncertain; the spelling is conventionally associated with the meaning of fluidity or wantonness.