DfT research indicates taht about 440 people are killed and almost 6000 seriously injured every year in crashes involving someone driving for work. It is important that drivers understand how small impairements can have a massive effect on their ability to drive safely.
The human body loses and needs to replace 2 to 3 litres of water on a daily basis. However everyone is different and there are a lot of factors such as weather, activity etc. that influence dehydration rates. A Loughborough University study shows that even mild dehydration is equivilant to being over the drink drive limit in terms of driver error. Driver education programmes should encourage appropriate hydration practices.