Nobody knows where the blob of water came from. But it's clear that it continuously searches for water, which it joins to it's body in order to grow. While it's taken over 300 years to go from a drop to the size of a human, dry spell overheard talk of a stream that ran to the ocean...

Strength

Ability to absorb water and grow.
Not affected by human weapons.

Strength Source
Natural ability of body.