The answer to the question “What about water?” depends on the context.
(1) In terms of general health, for generally well people without special circumstances, the focus on pushing to drink high amounts of fluids is misplaced. Make use of your internal regulating systems. To do this, first consider whether there might be any reason to wonder if your innate water-balance control is working properly. For example, people with reduced alertness or reduced perception of themselves may not respond as well to thirst signals,such as may happen with an elderly person who is more frail and showing signs of reduced self-care.
Your water-balance control system works best with water. Sugar-sweetened beverages seem more refreshing in the first moments of drinking them because they stimulate saliva secretion, which floods more fluid volume in the mouth and this sudden flow of saliva also would help clear any saliva sitting in the mouth that had become a bit drier or thicker. This part of the perceived “cleansing” effect. But, it is your own internal fluid stores that give you this. In a way, companies that sell sugar-sweetened beverages are “selling you your own saliva”. I don’t know if this interferes or not with the ideal functioning of your internal water-balance system. But it is a costly (money and health) way of hydrating yourself, when plain water will do just as well.
“No, You Do Not Have to Drink 8 Glasses of Water a Day”
(2) for athletes, the focus on pushing hydration, including the focus on sugar + electrolyte special “re-hydration” beverages, has been wrong-headed and much harm has resulted.
(3) for those looking for tools to help with weight control, there is limited evidence about what might be best. As ever, there will be no universal “best” answer and each person will have to combine insight from research with insight from their own individual needs and responses.
This is a report from a recent study. Note that this is a small study and of brief duration (brief compared to the years needed to see whether short-term changes are carried forward in time – the body has a great talent for eventually shifting its function to counter-balance for any specific targeted tricks such as this).
Also note that the water (yes, plain water) was specifically timed for shortly before meals. The researchers were not trying to study a general effect of fluid intake over the days and they were not studying the state of hydration of the participants. They were speculating as to whether plain water right before meals may have an effect (of any sort) that would show up as greater weight loss. The study authors call it “preliminary evidence”.
Newspaper report: “A pint of water every day is the key to losing weight, scientists say” LINK from The Independent, Aug 28, 2015, by Caroline Mortimer.
Study: “Efficacy of water preloading before main meals as a strategy for weight loss in primary care patients with obesity: RCT.” LINK to abstract.
“All participants were given a face-to-face weight management consultation at baseline (30 min) and a follow-up telephone consultation at 2 weeks (10 min). At baseline, participants were randomized to either drinking 500 ml of water 30 min before their main meals or an attention control group where participants were asked to imagine their stomach was full before meals. The primary outcome was weight change at 12-week follow-up.”
“Adjusting for ethnicity, deprivation, age, and gender resulted in the intervention group losing -1.2 kg (95% CI -2.4 to 0.07, P = 0.063) more than the comparator”
The numbers given for the amount of weight loss in the newspaper report compared to in the abstract are confusing. The extra weight loss of -1.2 kg was an average for all the water-group participants, no matter how well they had followed the instructions about the water intake. When the researchers considered only those participants who had regularly consumed the 500 ml (about 2 cups) before meals three times a day, the amount of weight loss was much more.