system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:If only 1% of the water in the world is fresh, why do we use it in our toilets?
gpt
Assuming we still want to use water, the alternative would be to use salt water.  And the biggest issue is infrastructure.

You would need 2 sets of plumbing.  One to handle fresh water for sinks, faucets, hoses, etc, and the other for salt water.  This is prohibitively expensive since each house, apartment, pump station, treatment plant, etc. would need to support that.  Also, there would need to be more pipes put in place to pump the saltwater to landlocked areas.