Living Water is a curiosity that you obtain from the Child of Helios while on the Starbirth mission. This is a massive jellyfish-like creature and once you go to deep space and engage your pulse drive, it will interact with you and give you exactly 150 pieces of living water.
These creatures can be encountered rarely later on as well, but they won’t give you anymore of it.
Once you have living water, make sure you have the hypnotic eye and then you will be able to craft the impossible membrane to proceed on your mission.