system
Given the following post, respond as if you're commenting on Reddit:
human
Why can't we use salt water in our toilets? 

Would the salt erode the pipes at an alarming rate?
gpt
The plumbing issue is minor, and can be countered with an appropriate choice of materials.  Boats and ships use saltwater to flush their toilets all the time since its readily available unlike fresh water.  However, on land you would need to run both a saltwater supply line **and** a second saltwater sewer line at massive expense.  

This is because sewer waste is treated before discharge, and combining salt and fresh wastewater would result in brackish sewage that couldn't be discharged in normal locations.  *If* you had a septic tank, you would be salting your fields.