It is sunnah (preferable) to open the fast with and odd number of dates, and if they are not available, then with a sip of water
Salman ibn Amir reported that the Prophet (s) said: “When one of you is fasting, he should break his fast with dates; but if he cannot get any, then (he should break his fast) with water, for water is purifying.” [Sunan of Abu Dawood Hadith 2.2348]