Water pollution due to something like soap is tricky.
According to the Challenge, your team has to start with "a piece of trash" and then follow it to see how it is handled.
Note the box labeled "Exceptions": waste water is not valid trash for this Challenge. That's certainly a significant way for soap to reach the ocean. Your team's project can't start with waste water.
On the other hand, look at the project update from August 27th. There might be an alternate way to look at it that would provide a meaningful problem.
Virginia-DC FLL Referee Advisor