There's No Official Evidence That Water Controls Dehydration

According to an EU regulation:

They applied for the right to state that “regular consumption of significant amounts of water can reduce the risk of development of dehydration” as well as preventing a decrease in performance.

However, last February, the European Food Standards Authority (EFSA) refused to approve the statement.

A meeting of 21 scientists in Parma, Italy, concluded that reduced water content in the body was a symptom of dehydration and not something that drinking water could subsequently control.

In a related story, a few years ago, an article in the British Medical Journal pointed out that:

As with many interventions intended to prevent ill health, the effectiveness of parachutes has not been subjected to rigorous evaluation by using randomised controlled trials.

I thought that was intended as a joke but now I'm not so sure.