Many people believe that drinking water plays an important role in weight loss. That it either somehow helps weight loss directly by impacting on metabolism, or indirectly by making a person feel fuller and therefore less likely to overeat. Unfortunately neither of these mechanisms are true.
That said, water, and really any zero calorie beverage, can be useful to weight loss if it’s consumed in place of a caloric beverage - most notably, sugar sweetened ones.
When it comes to research on the impact just drinking water has on weight loss, it’s not particularly exciting. One study looked at the impact purposely drinking 500, 1000, 1500, or 2000ml of water in the morning before an all you can eat lunch buffet to see what impact that would have on how much a person ate. Even people drinking 2 whole litres of water didn’t see an impact on their lunch consumption.
Another study looked at the food diaries of people on days that they did and did not report water consumption. Again, no impact was found - people at the same amount on days they did and did not consume water.
As far as hydration and water goes, or put another way, do you really need to drink 8 glasses a day for health? The answer is not exactly, no. Assuming you don’t have a medical condition that directly impacts upon your ability to perceive thirst, the human body is exceptionally good at meeting its hydration needs. So yes, if you’re thirsty you should definitely drink. Ideally water because it has no calories and generally speaking caloric beverages don’t have health benefits that make their calories worthwhile or necessary. But as to how much you should drink (those mythic 8 glasses) - you should drink as much as you need to satisfy your thirst.
As to non-nutritive sweeteners, while it’s certain that less sweet from all sources (sugar and alternatives) is probably the best option health wise, if there’s a choice between a sugar sweetened beverage and an artificially sweetened version of that same beverage, if weight is a concern, and possibly even if it’s not, the artificially sweetened beverage is a wiser option. Given there is no compensatory dietary intake if a person’s liquids don’t contain calories, if the only thing you change is to replace all of your caloric beverages with zero calorie ones you might indeed expect to lose weight. The more calories you replace (meaning the more liquid calories in your baseline), the greater the impact. This is of course true for calories coming from alcohol as well given drop per drop for instance wine contains double the calories of most sodas.
As to how to ensure when it’s an option you drink water instead of sugary beverages? Bring it with you. Pretty much all venues and businesses will have taps and water dispensers for you to use, but many won’t offer bottled water in place of sugary fare. If sweet is a need for you, consider also packing a small bottle of concentrated/flavoured artificial sweetener that you can add to water to increase your enjoyment if sweet is your thing.
If your aim is significant weight loss, while water may play a small role, unless you’re drinking litres of soda daily, water alone is unlikely to get you where you want to go. It’s too bad too as if water consumption had a major impact on weight, there’d be far fewer people struggling with it.
