Any planet with open water, but preferably with a TL of 8-9 or so (or lower, for even more fun).
For some reason, the PCs must have chosen to attempt wilderness refueling in an ocean. Also, the ship should be slightly battered. In my campaign, a previous encounter with a hostile spacecraft accomplished this.
While refueling and surveying damage, lots of alarms keep going off all the time. This started during descent to the planet surface, but it keeps getting worse. Collision alarms, pressure failure alarms, power failure, and so on. Keep interrupting everything the PCs do until one of them gets annoyed enough to shut off the alarm reports.
In case you haven't guessed, there is a lesson in here somewhere.
Then, have some airlock in a rarely used part of the ship begin leaking water. Slowly at first, but then faster. It will quite possibly take some time until the PCs discover this. Especially if they are kept busy repairing stuff in other parts of the ship and have no business in the lower cargo holds (or wherever the leak is located).
Sooner or later, have them notice odd sounds (from the water moving when the ship rocks back and forth) and smells (from algae and other stuff in the water). When they discover that there is a meter or so of standing water in their cargo hold, they are going to get pretty upset.
Possible directions to take this adventure
- Everything is OK, just lifting the ship out of the water will solve the problem. There will still be a lot of repair work to do, but the crew are lucky that the leak was this minor (and opened during landing in the water, not in space).
- As above, except the water leaves a nasty smell and some odd molds or fungi.
- As above, except some water has gathered in holes in the cargo hold floor and will need to be scooped out by hand. Hard work, and you really want to shower afterwards. Which can get funny if there are less freshers on board than PCs helping in cleaning out the cargo hold.
- As above, except some harmless animals have slithered in through the airlock (which malfunctioned and opened). This is ideally noticed by someone wading through the water to inspect damage, and should make for a nice and scary effect.
- As above, except the animals aren't harmless. Some kind of fish with sharp (and poisonous) fins has moved in, causing the situation to become more problematic that above if someone does something stupid (i.e. moving out into the murky water without protection).
- As above, except some kind of large squid-like creature is examining the ship from the outside, probing the opening with its tentacles. If someone moves out into the murky water, that person is in for a nasty surprise (think Star Wars trash compactor).