I'm not the dev but from what I've seen, it's a bug.
There's no way the fact that the water collector gives "free water" is intentional.
As for a little more insight :
A single Water Collector gives +1 Water per seconds.
For now, I'm going at +10 water per seconds with 10 Water Collectors.
It can only be a bug since the water is almost absolutely useless right now. I have 250+ ice patch in my storage waiting to be used and I already made 50+ Oxygen Bottles..
I think it could be a good idea to increase the rate of seed drop while harvesting greenhouses, or at least having 2 seeds per drop instead of 1.
Right now I have 15 greenhouses and there's rounds where the 15 plants doesn't even give a single seed which is.. Kinda sad when you think about it. Big farms are useless at this state of the game.
I don't think it'll be good to have a really high drop pourcentage as it will be way too overpowered and will defeat the goal of the game to "explore".
For now greenhouses are more like "bonuses" if you ever need to craft food.
Since you can at least survive for a good 150+days without having to go really far from your base (Stew giving 1day of food)
I..am not sure why you really want to take water out of the Water Supply, since you actually put the water in it in the first place. (Unless you want to abuse the Water Collector + Water Supply bug :D) It's pretty much the player who has to manage properly their drops if you want my opinion. If the ice/water was being wasted after being in a storage for several days and you "had to" put it in a Water Supply to keep it fresh or something then I would understand.
Right now you can just stock your water in a storage and use it in a Water Supply if you want to supply your greenhouses in water.
If being able to take water out of the Water Supply is "adopted", then I think it should ask for a certain item for being able to "take back" the water.
Like "Okay, you did a wrong move putting water in it. Pay the price."
Quite good ideas, I think. It's great to see other players being invested in this game :D
PS : I'm sorry if I can sound rude or anything, It's not my native language and i'm trying my best to give good arguments !