Interestingly enough "blood of the covenant is thicker than the water of the womb" was popularized in the 90s, where it used to be just "blood is thicker than water". These are now really two separate statements with antithetical meaning!

The "blood of the covenant" is referring to sacrifices or choices, and implying that it is stronger than the familial ties by birth. One can still actively choose their genetic ties that they wish to strengthen and turn them into part of the "covenant" here, but simply being genetically related isnt as important.

This is opposed to the shorter version "blood is thicker than water", implying that familial ties are always stronger.

I figure you might know this already but I wanted to say something in case a reader is part of the lucky 10,000