Because you need salt and the drip provides it at about the level usually found in blood.
A little sodium – otherwise known as salt – is essential for muscle and nerve activity.
The reason we’re told its unhealthy is that most people eat too much, taking sodium above the healthy level of 135-145 milliequivalents per litre of blood.
Salt makes your body hold on to water, Blood Pressure UK explains.
“If you eat too much salt, the extra water stored in your body raises your blood pressure,” it says.
“So, the more salt you eat, the higher your blood pressure. The higher your blood pressure, the greater the strain on your heart, arteries, kidneys and brain. This can lead to heart attacks, strokes, dementia and kidney disease.”
As for the drip itself, its main job is to give you fluid – and the drip gets it into your blood faster than drinking.