What is Ramadan?
Ramadan refers to the 9th month in the Muslim calendar. Every Muslim is expected to fast during the day for the entire lunar month. During the month of Ramadan, Muslims all over the world abstain from food, drink, and other physical needs during the daylight hours. As a time to purify the soul, refocus attention on God, and practice self-sacrifice.
Fasting during Ramadan is strictly adhered to in places where population of islams outnumbered other religions. Such places in East africa includes Zanzibar, Tanga, Kigoma (in Tanzania) and Mombasa, Lamu, Malindi (in Kenya)
Non-Muslim tourists are not expected to fast even if the place they are visiting is predominantly Islamic. But, life in many Islamic countries changes quite significantly during Ramadan, which has both its pros and cons. Muslims in general are tolerant of tourists snacking and drinking during Ramadan, but be respectful of the fast and keep public consumption to a minimum especially in non-touristy areas. It is always a good idea to dress a little conservatively in Muslim countries and this is especially so during Ramadan.
By and large it's business as usual during Ramadan. Tourist sights like museums are all open, although they will often close earlier than usual to allow staff to get home and eat in time to break the fast. Public holidays to celebrate the end of Ramadan can close businesses and government offices for up to 3 days.
Restaurants catering to locals are often shut throughout the day during Ramadan, but they come alive and stay open after sundown until very late at night. You can still buy food and water during the day as most little groceries will be open and food markets continue to buzz. You'll see a huge rush of activity from about 4.30pm onwards as people buy last minute items to break the fast; sweets and pastries are especially popular.
If you like alcohol you're out of luck during Ramadan because many liquor shops (if they have them) simply close down for the whole month. Bars and hotel restaurants that cater to tourists may still serve alcohol during Ramadan, so you can still enjoy a cold beer at the end of a hot day, just keep it out of the public eye.