Origin
This proverb was first recorded about 1412.
Explanation
The people who are related have stronger obligations to each other than to the people outside the family. Family ties are closer than other relationships. It alludes to the fact that water evaporates without leaving a mark whereas blood leaves a stain. The original meaning of the expression is that the ties between people who’ve made a blood covenant are stronger than ties formed by “the water of the womb”.
Examples
If you ever need help, don’t ask your friends. Come home and ask us, your family. Blood is thicker than water.
My friends invited me to go camping on Saturday, but I have to go to my cousin’s wedding instead. Blood is thicker than water, after all.