"Blood is thicker than water" is a recognizable proverb that has surpassed the test of time. The generally accepted interpretation of the saying is that the bond of those related by blood is stronger than the bond of marriage or friendship. The origin of the saying is most often attributed to Scottish poet and novelist Sir Walter Scott in his novel “Guy Mannering” in 1815. Other, earlier sources include references as early as the twelfth century.
Some sources state that the expression was first mentioned in a medieval German beast epic by Heinrich der Glichezaere, which translated into English read “kinblood is not spoiled by water.” Other references mention a similar mention in 1412 by an English priest, John Lydgate, in Troy Book. More modern versions include Sir Walter Scott’s mention as well as those by authors Thomas Hughes, U.S. Navy Commodore Josiah Tattnall, and Aldous Huxley.
Various interpretations include Lydgate’s: “Relationships within the family are stronger than any other kind.” Huxley added a different twist with his interpretation in Ninth Philosopher’s Song in 1920 that “Blood, as all men know, than water’s thicker. But water’s wider, thank the Lord, than blood.” Tattnall is credited by some as the one who brought the proverb into common use when he used the expression in 1859 to defend the aid of his American ship to a British ship during an attack on the Chinese.
Other sayings are often related to "blood is thicker than water." These include bloodlines, bad blood and blood brother. "Blood brother" often refers to either two males related by birth, or two or more men not related by birth, but who swear loyalty to one another.
The phrase has obviously been in use for hundreds of years, with most modern interpretations in agreement that family bonds are closer than those of outsiders. In other words, those who are related by blood (relatives) are connected more intimately than those who are connected by water (non-relatives).
Whether Sir Walter Scott is to be considered the father of the phrase, he certainly has ties to many other colorful proverbs. He is recognized as coining other phrases in his writing to include cold shoulder, go berserk, lock stock and barrel, savoir faire, the apple of my eye, tongue in check and wide berth, among others.