Don't worry, it is generally safe. You can drink the bottled water definitely, but I would recommend you to drink from brands you recognize. There is one brand there called Hayat that has gotten me mildly sick every time I drank it, so I would avoid that one! Stick with ones like Nestle, etc. In my opinion Nestle tastes the cleanest and is the safest one.
As for the food, I would avoid any place that doesn't look too sanitary, a lot of the road side ones with really cheap food aren't too safe unless you are used to it. If you drink from any of the juice/sugarcane stands, ask for a paper cup because the glasses they serve it in usually aren't cleaned very well and are reused with tons of people throughout the day, so you can imagine... :)
If you want to be on the safe side, you can just eat from restaurants there such as McDonald's, Burger King etc. They are totally safe. I would avoid one called [Cook Door], though its delicious, even Egyptians complain about getting sick from it! :)
And just remember if you are in a restaurant and they bring you a cup with water in it, it is tap water, never drink it!
Hope you enjoy your time in Egypt, it's really a place I love. :)