We all know that this phrase. We have heard this many times especially when the topic is about being a family.
This phrase is a proverb that means a family's bond is stronger and more important than in any other relationships like friendship. It's used back since 12th century in the Germany.
There are many people saying/ stating that the original meaning/phrase of this is "The blood of the covenant is thicker than the water of the womb." which somewhat contradicts what we have been used to with the meaning of the phrase. It was said that it may not only be blood-related to be considered as "blood" but it's something about your strong bond as of like a family. Friends that you share a strong bond as if they are your 'blood' can also be considered. And even just a friend with strong bond(Blood of the covenant), it may be thicker than with a family member (water in the womb). If you read the original form of the phrase you can see that it has a different meaning than what we are used to believe in. It has a meaning that has been corrupted over the years, maybe in the Middle Ages when bloodline was all that's important.
In our lives, we have these special people that we share a connection and bond with as deep as what we are sharing to our family. And admit it or not, we sometimes feel that our relationship with someone not related (especially love/romantic) is stronger than the ties we have with one of our bloodline. There are also these relatives that treat you like a stranger and/or not important. We all know that we also tend to feel more stronger bond to someone else than with a blood-related individual. Romantic love for example.
No matter what the original meaning of this phrase is, I still think that family bond is so important that you should not take it for granted. And I also think that your relationship to other people may also be considered as a family bond when you share unconditional ties with them. Like with someone you love, care about and someone very dear to you.
May it be with a blood-related individual or not, you should always value people you care about. Make it equal as much as possible. There's no law stating you can't value someone else more if they're not blood related. Be good and value everyone and try hard not to make someone feel like they are less important just because they are the 'water' in the phrase.