Hana Kamkar, a famous singer, removed her hijab

A better question than what to drink to sing better is what to breathe to sing better. Although nothing you drink can directly moisturize your vocal cords, you can give your voice a boost by breathing properly humidified air. Overly dry air is very taxing on your breathing and your voice.
 Consider humidifying your home, especially when you’re working on a particular production or if you’re doing a series of concerts. Using a humidifier can support your respiratory health while also preventing dry vocal cords.