Not drinking enough water can make you very ill. Severe dehydration can lead to dizziness and collapse. If you are showing any signs of dehydration, drink some water straight away. Seek medical advice if you still don't feel better. Older people are at greater risk of dehydration because they naturally feel less thirsty. Their kidneys may also not work as well. Memory problems and not being very mobile can make it harder to stay dehydrated. Certain types of medicines such as diuretics and laxatives can also lead to dehydration. For older people, not drinking enough water over a long period of time can lead to problems such as constipation and confusion. Signs that you are dehydrated and need to drink more water include: feeling thirsty dark coloured urine headaches dry skin, tongue and mouth tiredness irritability light headedness or fainting Dehydration in babies and children can be serious and needs immediate medical attention.