Not overnight, drink it on the same day.

Fishwort water contains many fisetin, volatile oil, quercetin, potassium chloride and many other material components, generally is not recommended to drink fishwort water overnight, after a night time precipitation, which may be some of the components change, producing harmful substances. Secondly, overnight fishy grass water is prone to breeding bacteria, dust into the water and so on, so it is recommended that fishy grass water drink the same day, up to one day.