I'm not sure whether this issue has come up for me before now. Every time I get the 'Water a Plant' task as a scientist, the action doesn't remove the task. It's the only task which I can't execute. It stays pinned no matter how many plants I water.
I replaced the default pots in the laboratory with the wooden box that holds four plants. I was going to try placing a plant outside or in the default round single-plant pot, haven't tested it yet.
No mods or anything else changed, just the standard game with most of the packs installed.
Edit By crinrict: Added Tag to Title, Adjusted Title, added missing thread tags.