Depends on the cause. Some yiu can't prevent due to existing disease , hormonal imbalance. However, most causes is dirnking too much water which may be due to another condition, so a diuretic would take the water out, balancing the salt and water more. Or the body not filtering out the fluids. I'm curious have they been in the hospital. If that's the diagnosis, the person should have been told what to do. How old is the person and what medications do they take, what diseases do they have? Either organ or hormonal

Ps I have not experienced it