Tetanus inoculations are a good idea. Other recommended immunizations are for typhoid, tuberculosis, and polio. Gamma globulin shot provide protection against infectious hepatitis. Water is considered potable in most large cities but it never hurts to treat the water first, particularly if you are susceptible to stomach ailments. Bring along your favorite medicine for these symptoms just in case.
Bottled water is available at most hotels and lodges.
You may want to take one of these with you on safari drives to avoid dehydration, especially on hot days. Fresh water in much of Africa contains the parasite bilharzia . There is no inoculation, so it is best to avoid swimming in untreated water. Stick to the hotel swimming pools. Nairobi and Mombasa have modern hospitals, and most smaller towns have health clinic facilities.