It seems that it can be called sahoor, if one cannot find food, because of the hadeeth: “When one of you breaks the fast, let him break it with fresh dates, and if he cannot find any then with dry dates, and if he cannot, then with a few sips of water.” If a person does not have any food available, or he has food but he does not want to eat it so he drinks water, then I hope that this will count as following the Sunnah. End quote. 

Shaykh Muhammad ibn ‘Uthaymeen (may Allaah have mercy on him).