When you say 'goes through me', well, unless you have the squits, the water must have hydrated you as the kidneys only remove fluids to form urine from the blood.
Only something that is diuretic (which incidentally beer isn't) can signal an increase in urine production without a corresponding increase in hydration levels.
Absorption occurs from the final part of the intestine / bowel region, so sports drinks that claim to 'speed up hydration' do so by increasing the speed at which the fluids are released from the stomach and pass through the early part of the intestine en route to the absorption zone. (Note: if trying to use a drip on a severely dehydrated patient where the veins have collapsed, you take the needle off the end and shove the tube up their arse. Gets fluids to the important part of the gut far quicker than by mouth)
Diarrhoea is the only indication that absorption itself is not happening, (hence the danger of tummy trouble in the tropics).
What you are perceiving to be dehydration the following day is either because you were massively dehydrated and there is only so much fluid (of any type) the body can absorb per hour, especially when asleep, (hence the use of drips on the TdF), or you worked really hard and you still have need to flush a lot of waste byproducts from your system).
One reasonable indication of dehydration levels (in addition to urine output and colour) is to weigh yourself before and after an exercise session. Any weight loss in kgs is the number of litres you have lost through dehydration.
The best remedy for all this is not to get dehydrated in the first place. One bike bottle an hour is about what can be absorbed, so keep up that intake before, during, and after exercise. Only when it's really stinking hot should any deficit occur. This is particularly the case on a bike where carrying bottles is easy.
Remember a 2 percent drop in hydration will lead to a 10 percent drop in performance.
