I started suffering from leg edema (water retention) in 2018. Despite all the tests and remedies I tried, I couldn't find the cause or a cure. Then, a few months ago, YouTube recommended a lecture by Barbara O'Neill about the importance of drinking water. O'Neill based her claim on the findings of the Iranian doctor Fereydoon Batmanghelidj, who wrote the book Your Body's Many Cries for Water (1992). He developed his theory while in jail in Iran as a political prisoner, having only water to treat the other prisoners.
I started drinking two liters of water every day, and two weeks later, my edema was gone. See my before and after photos.
Now, if my legs get swollen, I know that I'm dehydrated. The swelling goes away once I drink water. Another side effect of drinking water was having fewer eczema flare-ups. It's incredible how simple and accessible the solution was for me, and I hope this knowledge might help more people.
