1. the leak in the sweet water system This is not a sentence. There is no verb. You can write: There was a leak in the sweet (fresh) water system.
2. the boat leaned to both sides I don't understand this. You can say, "The boat was unbalanced and rocked dangerously." the boat leaned over to both sides
The leak in the fresh water system (voulez-vous dire 'le système d'eau douce' ou 'le système d'eau potable'?) . Potable is the same word in French and English and it means the same thing. Fresh water is generally potable on a boat, but not always. It depends upon the degree of precision you seek.
The boat listed to starboard and port. The boat listed to both sides. The boat heel