Do low cal drinks substitute for water?

No, they're full of chemical sweetners!

I like to make jugs of herbal teas then allow them to cool, drink them with ice.

I love plain water and usually drink 12-24 cups per day, but I will also count anything caffeine free and less than 50 calories toward my water intake.

Chemicals and artificial sweeteners do not negate the hydration benefits.

A couple of great articles on the matter from the Mayo Clinic

http://www.mayoclinic.com/health/artificial-sweeteners/MY00073

Artificial sweeteners have been the subject of intense scrutiny for decades. Critics of artificial sweeteners say that they cause a variety of health problems, including cancer. That's largely because of studies dating to the 1970s that linked saccharin to bladder cancer in laboratory rats. Because of those studies, saccharin once carried a warning label that it may be hazardous to your health.

But according to the National Cancer Institute and other health agencies, there's no sound scientific evidence that any of the artificial sweeteners approved for use in the U.S. cause cancer or other serious health problems. And numerous research studies confirm that artificial sweeteners are generally safe in limited quantities, even for pregnant women. As a result of the newer studies, the warning label for saccharin was dropped.

Artificial sweeteners are regulated by the Food and Drug Administration (FDA) as food additives. They must be reviewed and approved by the FDA before being made available for sale. In some cases, the FDA declares a substance "generally recognized as safe" (GRAS). These GRAS substances, including highly refined stevia preparations, are deemed by qualified professionals based on scientific data as being safe for their intended use, or they have such a lengthy history of common use in food that they're considered generally safe and don't require FDA approval before sale.


And

Although it's a great idea to keep water within reach at all times, you don't need to rely only on what you drink to meet your fluid needs. What you eat also provides a significant portion of your fluid needs. On average, food provides about 20 percent of total water intake. For example, many fruits and vegetables, such as watermelon and tomatoes, are 90 percent or more water by weight.

In addition, beverages such as milk and juice are composed mostly of water. Even beer, wine and caffeinated beverages — such as coffee, tea or soda — can contribute, but these should not be a major portion of your daily total fluid intake. Water is still your best bet because it's calorie-free, inexpensive and readily available.
http://www.mayoclinic.com/health/water/NU00283/NSECTIONGROUP=2

Sprite Zero, Diet Coke and Pepsi Max, which are, after all, just fizzy water with a bit of flavouring!

Um...no. I do enjoy sodas too, but do not consider them as water. I log everything I drink separate from my water, whether it be diet soda, tea, coffee, or another drink.

And as for alcohol being considered water - I disagree. Alcohol is a diuretic, just as coffee is. It has no health benefits to it (save for red wine), and does not aid in hydration.

How you log it is up to you, but the benefits of hydration is a different matter.

Yes, alcohol and caffeine are both diuretics, but so is plain water. At some point, the benefit of drinking alcohol for hydration is outweighed by it diuretic quality but one drink won't dehydrate you.

Caffeine required you consume a huge amount before it affects hydration.

Sprite Zero, Diet Coke and Pepsi Max, which are, after all, just fizzy water with a bit of flavouring!

Um...no. I do enjoy sodas too, but do not consider them as water. I log everything I drink separate from my water, whether it be diet soda, tea, coffee, or another drink.

And as for alcohol being considered water - I disagree. Alcohol is a diuretic, just as coffee is. It has no health benefits to it (save for red wine), and does not aid in hydration.

All thin beverages should be considered equivalent to water for hydration effects. The diuretic effect of alcohol and caffeine is so small that unless you are drinking something designed to hold maximum amounts of either (e.g., 190-proof Everclear or barely-dissolved no-doze capsules) then the main component of the drink is water itself. Beer, wine, coffee, tea,soft drinks, etc. can all be safely counted toward "water" consumption, though some of these rack up significant calories.

As an aside, the whole "8 glasses of water a day" thing is just a health myth with no validity to it, anyway. The number is based on a study that recommended a certain amount of water consumption per calorie of food ingested. This rate, combined with a "standard" 2000 calorie diet led to about 64 ounces of water -- or 8 glasses. However, this doesn't account for the water content of the food itself, which certainly does count in your body.

If you want to drink lots of low-calorie liquids because it helps you feel more sated, then go for it, but don't think that you need to drink this much in order to maintain some healthy level of hydration.