Blood is thicker than water.

The proverb means that the bonds of family are stronger than any other: when it comes to a choice, kin will side with kin. It is said to explain a loyalty, to excuse one, or to remind someone of their first duty, often with a shrug, since it describes how people behave rather than how they should.

It is old in English and has an exact parallel in German, where “Blut ist dicker als Wasser” is equally proverbial. Walter Scott put a Scots form of it into Guy Mannering (1815). Spanish says “la sangre tira”, blood pulls, for the same instinct.

A claim that circulates online, that the “original” proverb ran “the blood of the covenant is thicker than the water of the womb” and meant the opposite, has no historical basis: the saying has always been about kinship. Its bluntness makes it useful and easy to contradict at once: many people find chosen friends closer than relatives, and the proverb is often quoted in order to be argued with.

English proverb