How much water should i drink everyday if i am dehydrated and have a virus?

Generally speaking : 8 - 10 glasses a day. While it is true that not everyone needs 8 glasses a day, most people do. You need more water when you are dehydrated and when you are sick. If you are quite dehydrated, then you probably need even more. In that case, you should drink fluids with some electrolytes and even a little sugar - that will help the water get into your cells where it is needed.