system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is saline the default hydration method for IVs and not just regular water?
gpt
Fluid in your body has an average concentration of 0.9% NaCl so it is most effective to hydrate a person with this type of fluid. If regular water is used it will disrupt many cells in your system. 

Basically it is easier for your body to take care of saline.