One of the main things I was told that helped in my remission from depression was - you can't pour from an empty jug. They explained that, like on an aeroplane, you put your own oxygen mask on before you help anyone else. If you don't look after yourself, you won't be able to look after those around you. Please try to drink some more. Your body is made up of a huge amount of water, and during the day you lose a huge amount by just breathing, being in a heated room and going to the loo. If you don't replace all this water, your brain can become dehydrated and cause low moods.
Lecture over!