The fourth pillar of Islam is to keep Ramadan. We try to respect the major holidays of our religious community, so we should respect Ramadan. Muslims fast by not eating or drinking during daylight hours. In my opinion, not eating and avoiding drinks with calories is good enough to respect Ramadan. Thirst is quite distracting and can interfere with concentration, so I recommend avoiding thirst. But of course don't drink publicly.
Islam has another holiday that happens to be the same as an Old Testament holiday, so this is also worth keeping. This is Ashura which matches Yom Kippur.