The hospital pumps its own water from bore holes, which provide safe clean drinking-water all year round.
Outside of the hospital compound, it is best to be more cautious, but bottled water and soft drinks are easily available at the many shops and stores. Mosi, the national lager is cheap and tasty, although most Zambians (when then can afford it) drink the more cosmopolitan Castle lager from South Africa.
The Doctor’s Mess at SFH proivdes three meals daily to clinical staff and students, and bakes it’s own bread. The food is usually good - but the menu is fairly limited, so that after a week or two you will probably want to occasionally cook for yourself or eat elsewhere.
It is always possible to buy fresh vegetables from the Chada (small shops and market stalls next to the Hospital) and Katete, although the range can get very limited at certain times of year. You can also buy good beef, “Hungarian” sausages and chickens from the Stores, along with various tinned goods. Maize-meal is the staple carbohydrate of Zambia, but potatoes, rice and pasta are all available if you search them out.
There are a few good places to eat around Katete (eg. Tikondane Guest House) serving traditional Zambian fare which consists of nshima (a bland but very filling maize-meal dough) with “relish” made from stewed meat, vegetables or beans.