What is a water cut?

In one line

A water cut is changing how much water you drink just before a bodybuilding contest to reduce the water in the body, so the muscles look sharper.

What is a water cut?
What it means to 'drop water' before a contest
Right before a bodybuilding contest, some competitors drink very little water on purpose. This is often called a 'water cut' or 'water manipulation'. This post explains what it is meant to do and what happens in the body.
In one line
Trying to reduce body water just before a contest
A water cut means sharply changing how much water you drink starting a few days before a contest, to reduce the water in the body. It is one part of getting ready in the last week before a contest, called 'peak week'.
Background - where body water is
About 2/3 inside cells, 1/3 outside
Water in the human body sits in two main places. About two-thirds (2/3) is inside cells, the tiny units the body is made of, and the remaining one-third (1/3) is outside cells. The water outside cells is further split into water filling the spaces between cells and water in the blood.
Why do it
The idea that less water under the skin looks sharper
Competitors believe that if the water just under the skin goes down, the borders between muscles look sharper. A body that looks like its water has been squeezed out is called 'dry'. A water cut is an attempt to remove this water under the skin.
How it is done
Drink a lot, then cut back sharply
A common way is to drink far more water than usual for a few days, then cut back sharply as the contest gets close. The idea is that the extra urine from drinking a lot will keep going for a while after cutting back, so more body water is lost. Salt intake is sometimes changed at the same time.
How common is it
Two in three competitors drank more water
In a survey of British natural contest competitors, about two in three drank a lot of extra water on purpose in the last week before a contest. Water manipulation was the most common preparation after carbohydrate manipulation.
Diuretics
Banned drugs used to drop water
Competitors have been reported to use diuretics to drop even more water. Diuretics are drugs that increase urine to remove water and salt from the body. The World Anti-Doping Agency (WADA) bans diuretics at all times, in and out of competition, and the International Federation of Bodybuilding and Fitness (IFBB) follows its code.
Risk 1 - dehydration
Not having enough water in the body
Not having as much water as the body needs is called 'dehydration'. As it gets worse, it causes dizziness, a fast heartbeat and confusion. Severe dehydration is a life-threatening emergency.
Risk 2 - real cases
Taken to the emergency room during or after a contest
There are reports of competitors who sharply changed water and salt and also used diuretics, and were taken to the emergency room during or right after a contest. Their blood 'potassium' (a mineral muscles and the heart need to work properly) went too high or too low, causing muscle paralysis or heartbeat problems. A competitor who died after using similar methods has also been reported.
Common misconception
Does cutting water only remove water under the skin?
No. Body water moves in and out of cells to stay in balance, so it does not leave from just one chosen place. Even in an experiment where people lost weight by sweating while exercising in the heat, water in the muscles dropped along with water in the blood. So the water inside the muscles that competitors want to keep is lost too.
Summary
Trying to reduce body water just before a contest
A water cut means changing how much water you drink just before a contest to reduce body water. Water does not leave only from under the skin; water inside the muscles is lost too. Related terms: peak week, diuretics, carb loading.