Your pee should be very pale yellow, if it is darker than that you are not drinking enough. It does not have to be water it can be tea, coffee, juice ,milk it all counts as water. My wife just had a urine test and the doctor told her off as her pee was too dark, he said it meant she was not drinking enough fluid.
I also have a "soft spot" for Eddie's answer.......drink enough during the day to keep your urine pale yellow. Don't worry about it being dark first thing in the morning, that is quite normal.
I keep hearing reports of this heatwave but nothing like that up in Manchester, is it really hot down south then? Just cloudy and muggy up here but seen the awful reports of the crash on the news down south, something to do with fog?
I think everyone is different and it can make a difference how much liquid you are also getting from your food. I drink a lot though I'm thirsty all the time and have a really dry mouth. I find if you carry a drink like a bottle of water round with you then you have it available whenever you feel thirsty, more if you are sweating fluids out such as when it's really hot or you're working up a sweat such as exercising.