How much water can I fill a boeing 747 full of? (And it still be able to fly)?

Ignoring the insanity of flying water to Africa why bother when most countries in africa have lots of water, water is not a problem. Supplying and making clean water is a problem in a very few countries but actually having water is not an issue. If you want to help those vey few poor countries in Africa then sending over some money to build decent water reclamaition plants and sewage treatment works would be a far better idea. Also don't forget that Egypt, morrocco, Kenya, South Africa, mozambique, Tunisia are also African countries and have no problems at all with water, health care, tourism, industry, decent schools, wonderful universities, a vibrant technology base, a decent police and medical service etc... Africa THE CONTINENT has no real problem at all, Some COUNTRIES IN AFRICA do have problems but then so do some states in the USA, sometimes worse than in the poor countries in Africa.

But back to your question... you could put about 2 million liters of water in a Boeing 747 but the cost of flying it all the way there would mean I'd be paying 5 dollars a liter. It would be cheaper to import Evian bottled water and hand it out with a straw.