水虱草（学名：Fimbristylis miliacea）为莎草科飘拂草属下的一个种。

Fimbristylis miliacea, the grasslike fimbry, is a species of fimbry that probably originated in coastal tropical Asia but has since spread to most continents as an introduced species. It is a widespread weed in some areas and is sometimes problematic in rice paddies.