I don’t actively use it, but my Garmin 530 does estimate the amount of water consumed based on effort and duration. I think it might take ambient temperature into account too, but not sure. I think you can calibrate it for your personal consumption too. I do have a power meter and HRM with my training zones calibrated, which it probably needs for this. I should check it out really, but I’m pretty good at keeping hydrated on rides. All I notice is the estimation of consumed bottles in the ride summary. I don’t have the drink alarm set up.