Hanging in Gnawing Lerker area. Same height as the power cell. It is easy to shoot and find.
On the way to the Robot area. It is harder to shoot, easy to hit, and easy to find.
Near Dark Cave entrance. It is easy to shoot and find. Use platforms to hit.
Near Dark Cave entrance. Cross Dark Eco with platforms. You should be able to find some clean water on the other side of some Dark Eco. You must use the rolling jump (L1 or R1 and jump when you finish rolling) or you cannot get across the Dark Eco. Swim down and get close enough and it will explode. It is difficult to get to.
In Dark Cave, after you pass the second hanging spider and before the first rotating platform. Near the crystal that is after the second spider, you can find some clean water. Swim down and get close enough and it will explode.