Keep up with drinking a lot of water.  To answer your question let me pass on some information and you can make your own informed decision.

Carbonated diet cold drinks contain phosphates and aspartame.

Phosphates suppress calcium absorption and increase bone loss by having an activating effect on parathyroid hormone (the hormone that stimulates calcium resorption from bone).  Consumption of this beverage may be a factor in the development of osteoporosis.

Carbonated beverages can also exacerbate a condition known as GERD (gastroesophageal reflux disease), which has been linked to oesophageal cancer.  Some carbonate in the stomach increases the secretion of gastric acids and promotes absorption of liquid by the mucus membrane, increasing the effect of alcohol.

Aspartame (L-a-aspartyl-L-phenylalanine methyl ester) is a sugar substitute frequently used to sweeten a wide variety of diet cold drinks and foods.  Aspartame is approximately 200 times sweeter than sugar, tastes like sugar, saves kilojoules and does not contribute to tooth decay. Products sweetened with aspartame can be useful as part of a low kilojoule diet.

There have been reported cases of adverse and side effects of aspartame but aspartame has not been carcinogenic in experimental studies and no clinical studies have found proof of ill effects in humans consuming large doses.

Carbonated diet beverages can never function like the regular pure form of water. There is no replacement to pure and regular water.  Carbonated diet beverages also contain no nutritional ingredients that can benefit your body. Thus it is advisable to stay away from these drinks and stick to more natural sources of fluid.

Fruit juice is highly concentrated in sugar.  The sugar content of one glass of fruit juice is almost equal to three fruits.  Therefore fruit juice should be drunk in moderation.  Rather eat the fruit than drink the fruit.  Or rather eat the fruit and drink the water.