Avoid anything in excess
I am an Ayurvedic Doctor and fully agree with the point that Usha Paan is not good if continued for long. Ayurveda has mentioned Usha Paan in particular disease/condition which doesnot mean everyone should start drinking water early in the morning. Considering ayurveda concepts of Agni (Digestive capacity), jala(water) is having properties opposite to Agni hence excess of water will disturb/reduce your digestive capacity & hence lead to many diseases & people who say that excess of water will flush of your intestines should study anatomy first as the process is totally different then what these people explain & not just a drain pipe where in you pour water from one side & drain it fron other side but that entire water has to be absorbed, filtered in kidney & then thrown out.
But still in some conditiones Usha paan has been advised and that therapy should be related to that specific condition/Disease and not anything else