The otherwise unread proverb will have the sense, that the bond of blood is not broken, and thus the son of Diezelin has taken up his father’s beliefs.

(“I hear it also said, that kin-blood is not spoiled by water”.) No evidence is given that the modern proverb traces back to this version, which Grimm says is “sonst nicht gelesene”, that is, not found anywhere else:

“The oldest record of this saying can be traced back in the 12th century in German.” The only evidence presented for this claim is these two lines from the poem Reinhard Fuchs (c. 1180) by Heinrich der Glïchezäre:

“By 1670, the modern version was included in John Ray’s collected Proverbs.” This is false, as discussed above: the proverb first appears in the fifth edition (1813) of this work.

“Modern commentators, including authors Albert Jack and R. Richard Pustelniak, claim the original meaning of the expression was that the ties between people who’ve made a blood covenant were stronger than ties formed by ‘the water of the womb’.”

Let’s take a look at the quality of these references. First, Jack:

The phrase ‘Blood Is Thicker Than Water’ suggests that family bonds of trust and loyalty are stronger than those friendships we make for ourselves. I for one have never believed this, and was unable to work out the ‘water’ connection until I started to look at the many biblical references to the phrase. In ancient Middle Eastern culture, blood rituals symbolized bonds that were far greater than those of the family. Hence the bond between ‘Blood Brothers’—warriors who symbolically share the blood they have shed together in battle—is far stronger than the one between you and the boy you grew up with who kept pinching your records. In addition, there is an expression dating back three thousand years that tells us: ‘The blood of the covenant is far stronger than the water of the womb’, which is a forerunner of the phrase we use today. In modern times, we understand ‘blood’ to be the bloodline of a family, but, as you can see, that is not the original meaning of the expression at all. Its meaning has thus been corrupted over the centuries, probably by the English nobility of the Middle Ages to whom the ‘blood line’ was all important. Albert Jack (2005). Shaggy Dogs and Black Sheep: The Origins of Even More Phrases We Use Every Day, p. 95. Penguin.

Jack gives no references for any of this, and several aspects of it are quite implausible. If there are “many biblical references” to the phrase, then why not mention the best one? The claimed meaning of “blood brother” is not any of the usual meanings found in reference works. An “expression dating back three thousand years” would surely have left written traces in that time. It is hard to avoid the impression that Jack is just making things up, especially when you turn the page and discover his claim that the phrase “butter someone up” comes ultimately from a Tang Dynasty tradition “known as ‘buttering up the Buddha’”.

Second, Pustelniak:

“Blood is thicker than water.” This phrase has completely lost its original, covenant-related, meaning. Today, it is interpreted as meaning that blood-related family members are to be considered as more important than anyone else. However, the original meaning is, “The blood of the covenant is thicker than the water of the womb,” or, “My relationship with those to whom I am joined in covenant is to be considered of more value than the relationship with a brother with whom I may have shared the womb.” “…there is a friend that sticks closer than a brother." (Proverbs 18:24) The term friend has also lost its original meaning. More than an acquaintance, or one that I have some amount of affection for, it is actually a term to be used to refer to one with whom I am joined, in covenant. R. Richard Pustelniak (1994). ‘How Shall I Know? The Blood Covenant’. www.bac2torah.com/covenant-Print.htm

The web site bac2torah.com is run by Beit Avanim Chaiot, a Messianic Jewish congregation in Tucson, Arizona, and the page had the same text when the Internet Archive first captured it in 2010. There are no references.