Clarke, Finn, and Wells collect some plants for Jasper's wounds in a river in episode 1x03 "Earth Kills".
First Aid on Beach
Lincoln works to heal Octavia's arrow wound on the shores of a river in episode 2x01 "The 48".
Clarke washes ashore and is saved by Anya after jumping off the dam in episode 2x03 "Reapercussions".
Clarke fakes passing out and then attacks Roan while he is transporting her in episode 3x02 "Wanheda: Part 2".
Octavia is watching a group take water samples for Pike when a Grounder kid approaches in episode 3x06 "Bitter Harvest".