Maritime Safety and Emergency Procedures: IMO SOLAS, Lifeboats, Water, and Signals Practice Test

The key idea is that the first amount of rain to wash over a ship’s exterior carries the highest concentration of salts washed off from the canopy and other deck surfaces. When rain begins, seawater salts on the canopy and rails are dissolved into the initial runoff. If this first portion is collected and stored, it can raise the salinity and potentially other contaminants in the rainwater you’re trying to keep for use. By pouring that initial flow overboard, you prevent the salt-rich water from entering the storage system, leaving subsequent rainfall water cleaner for consumption or use. The other options don’t fit this common practice as well: oil or “dirt” can be present, but the specific reason tied to deck canopies is the salt washed off from the canopy. Testing cannot be the purpose in this standard procedure.