Dietitians & physicians almost always suggest people to drink more water but rarely suggest quantity or time(s). As no one likes to admit one's ignorance, even about such issues, nobody bothers to clarify with them.
It has been read that a healthy person has to drink water equivalent to 3 to 5 percentage of body weight, on an average day. On days of more physical exertion or sweating, one has to take proportionately more water. People who take some type of medicines also has to drink more water to wash out its residue.
That means a person of body-weight 50 kg has to drink 1.5 to 2.5 kg (or Ltrs) of water on a normal day under normal circumstances & more according to the circumstances.
An easy way to verify the adequacy/sufficiency of quantity of water intake, when coloured medicines are not taken, is to monitor the colour of urine. Under normal circumstances with sufficient water intake the urine will be practically colourless, like plain water. This is the ideal situation for the kidney. Shortage of water will increase the concentration of Uric acid type of chemicals & will damage the kidney in the long run.
Recently when a Urologist suggested my wife to take more water, she asked back "how much is the quantity meant by 'MORE'?" He was patient enough to explain it in a different way - in the Urologist's angle. He said: "Harmful bacteria like the Coli-form bacteria needs only three hours to reproduce. Hence take that much water to ensure that you are forced to urinate before three hours." This appears to be a very reasonable guideline, easy to follow for any one.
There is an easy way to get reminded about the quantity and times of intake. Collect sufficient number of empty bottles (available in plenty now-a days) sufficient to hold the water to be drank a day. Fill those in the morning & finish those before going to bed. For different people use bottles of different shape/colour, write names with non-washable marker pen or paste some stickers to distinguish.
Now about when to drink water. Most of Indian dishes contain sufficient water to digest it properly. So avoid drinking water from half an hour before to half an hour after (or till digestion is complete) and during food intake (except while having dry items like bread, roti, chappaathi, phulka, fried rice etc). Otherwise water will dilute the digestive enzymes & make digestion incomplete/imperfect/improper. This can lead to acidity & gas problems in due course.
It is true that drinking excess water at a stretch can tumble electrolyte as well as salt balance of the blood. It can be managed on Day 1 by taking a bit of salt-water, soon in case of any discomfort, and from Day 2 on-wards by reducing the intake quantity.
I do not feel that drinking the required quantity of water will tax the kidney by over-work & drinking less water is better. Drinking less/insufficient quantity of water will instead increase the concentration of chemicals that pass through kidney & damage it even in the short run.
DRINKING LESS WATER OR MORE WATER IS NOT GOOD. WHAT IS REQUIRED IS TO DRINK THE REQUIRED OR PROPER QUANTITY OF WATER AT APPROPRIATE TIMES.
Please correct me if I have gone wrong some where.