So, to simply this a bit for me ....
Is there a guide to roughly how much water I should drink say for every hour of riding? Or every 10 miles ?
As John says we are all different, though I'd have said a
bit different, we all follow the same rules of biology.
Sports nutritionists tend to recommend 500ml an hour during reasonable exertion, that's a decent starting point, you may find you prefer 300 or 700, but those are probably the extremes. Remember this is in addition to the 2 litres a day we're recommended to drink anyway. Also worth looking at what counts, tea, coffee, skimmed milk... and what doesn't.
It mainly trial and error, there's plenty of information you body is telling you, as long as you listen. If you find yourself feeling really thirsty, you've already left it too late, there's plenty of charts for the urine colour a well hydrated body will produce and if you don't find yourself needing to let some out every couple of hours, you're probably not drinking enough.
In hotter weather, you will need a bit more, but it isn't a huge amount, again trial and error, but for me it's around an extra 10%. Sweat isn't always a good guide, when riding it can evaporate so quickly you might not notice. it's easier to drink enough when it's warm, the inclination is there. What's harder is to get in the habit of drinking enough when it's cooler, and habit is what you're ideally looking for. Choosing drinks you'll want can be helpful here, a bit of flavour, tea in a flask...
If you don't drink enough, it can spoil your day, if you drink a bit too much the worst that happens is you need to stop more often to let some out. If you were at the elite level of athleticism, getting it perfect would be important, getting it about right is good enough for the rest of us.