Water Does Not Move on Its Own
The short answer
Water cannot set its own direction; it follows whatever pulls it. What the body does instead is keep separate doors for water to pass through, and decide how many of those doors to open. So swelling is less a matter of having too much water than of water having left the place where it belongs.
Contents
"If I drink a little less water, will the swelling go down?"
People who swell ask this often. But cutting back on what you drink does not take the swelling down much. I start the consultation by explaining why.
Water gets pulled about
Water cannot set its own direction. It only follows toward wherever there is more of what pulls it — salt, sugar, and the like.
So when the body means to move water, there is no way to push it. It moves water by where it puts the thing that pulls.
Letting it seep through would be too slow
Water can pass through a cell membrane by seeping, working its way in between the fatty components that make up the membrane. The trouble is the speed.
The kidney filters something like a hundred and eighty litres a day and takes most of it back in. Seeping cannot keep up with that.
So the body keeps a separate door for water to pass through quickly. It is a protein called aquaporin. When this door opens, water passes 10 to 100 times faster.
This door is particular
It is just wide enough for a single molecule of water, so it lines them up and lets them through one at a time. And it keeps salt from passing. It filters out charged particles, and hydrogen ions as well.
It is a structure that lets water through while keeping electrical signalling from leaking. The work that revealed the shape of this door was given the Nobel Prize in Chemistry in 2003.
Some kinds carry small molecules such as glycerol along with the water. Kidney, salivary glands, tear glands, sweat glands, brain, skin, the lens of the eye, fat, liver — more than ten kinds have been confirmed in the human body, and each place has its own.
The body decides how many doors to open
The collecting duct of the kidney keeps these doors stored in pouches inside the cell. When a signal comes saying water must be conserved, it moves the pouches toward the cell membrane and sets the doors in place. When the signal stops, it takes them back in.
Water only gets pulled along, but how many ways to open is the body's to decide. Rather than handling the amount of water directly, the body opens and closes passages and changes the circumstances.
So swelling is closer to a matter of place
Oedema is fluid that should be inside the vessels passing out of them and pooling between the cells. There are cases where the whole body's water has increased, but the swelling we commonly see is closer to a matter of place than of amount.
So cutting back on what you drink does not bring water that has already left its place back to where it belongs. That is my answer to the question at the start.
Which path that displaced fluid takes on its way out I have written down separately in Sweat Is Not Only for Cooling You Down.
So I do not aim at the water
When I look at swelling, rather than at draining water I look at the circumstances the water moves in.
Poria I take to bear on the movement of water in a way that does not much disturb the electrolytes. Since it appears to act not only in the kidney but on the water paths of the digestive tract, the surroundings of nerves, and connective tissue, I read this material less as a kidney medicine than as one that changes where the body fluid sits.
That much is what the material moves in the body. Where I actually use Poria in practice is more often the nerve side than the water side — settling a state in which signalling has left its place and grown, or keeps repeating itself.
What is interesting about Atractylodes is that its direction is not all one way. There are reports that it works toward opening the water paths in the intestine and toward closing them in the kidney. One material, then, using the same door in opposite ways depending on the place. What comes of this is not water being drained but pressure that had been bearing down being brought back.
Astragalus bears on holding the leaking side and returning fluid that has already left back into the vessels.
This much, though, is research at the animal and cell stage. It is not at the stage of being confirmed in people.
One door does not explain everything
I have told this at some length, but the water path is one route among many.
Gathering together materials that act on the same route looks as though it should make the effect larger, and it does not. They are absorbed at different speeds, metabolised at different speeds, and on the vascular and nervous side they either support one another or pull against one another. This is why the combinations long in use are worth something — they are pairings confirmed through experience to hold one another up when used together.
When to see a doctor first
If one leg suddenly swells, if swelling comes with shortness of breath, if the amount of urine drops noticeably, or if weight has risen sharply over a few days — before a story like this, examination and testing come first.
Sources
- Oedema — an account of fluid inside the vessels passing out and accumulating between the cells of the body — National Health Information Portal (Korea Disease Control and Prevention Agency)
- A piece setting out that water does pass through lipid membranes but not fast enough for many physiological processes, and that this channel is not a pump — The Journal of Clinical Investigation, 2002
- A review gathering studies on water-path regulation and herbal medicine, stating together that these remain at the animal and cell stage — Frontiers in Cardiovascular Medicine, 2025
Written by Dr. Heo Ji-young (Ph.D. in Korean Medicine Pathology, Kyung Hee University · former Research Professor of Herbology, Kyung Hee University)
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