One topic when talking about protecting the environment is that a lot of water is used in, for example meat. But isn’t water in a cycle within a closed system? I drink it / but it into plants or animals and after I consume it, the water gets released again.
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Even in a fully closed cycle, there is a limited amount of water available at any given time, and also only some water is in the stage of the cycle where we can use it.
Suppose that me and my tribe live under a glass dome with a closed water cycle. There is a total of 1000 liters of water in this dome at any given time. Any water that I use, whether it is to cook food, wash clothes, drink, or water my crops, will still be part of the cycle. However, while I’m using a given liter of water, my fellow tribespeople cannot use that same liter. If it’s in my cooking pot, it cannot also water my neighbor’s plants. Once I’m done with it, I may give it to my neighbor. Or, I may discard it and it will find its way back to the lake from which we both get our water, and then he can use it.
So, while no water ever gets used up (not permanently anyway), it’s still important how much water is in use at any given time. If our tribe’s water use gets out of hand, our demand might go beyond the 1000 liters that are in our dome. Now maybe I want to drink some water, but I can’t, because every liter of water is being used elsewhere. The fact that this water will eventually be freed up again is no good to me right now.
Also, even if we only use, say, 800 liters of water at any given time, the question is where the remaining water hangs out. If it’s in the lake, that’s fine because we can go there and collect it. But if it’s in the air, in clouds or water vapor, then we need to wait for it to rain. If it’s in the ground, we also may not be able to get to it. So, even if there is enough water under our dome in total, there may not be enough that’s actually available at any given time.
One important way in practice that water in the water cycle becomes unavailable is when it ends up in the ocean. While it is in there, we have practically no access to it, unless we expend a lot of energy to remove the salt from the water that we want to use. So in practice, we have to wait for the salt water to evaporate and rain down as fresh water again.
So yeah, in short, it’s all about how much water is available at any given time. The fact that water is in a closed cycle is no good to me if I need to wait too long for water to become available again, or other people always get to it before I can.
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