I don't know enough about Africa between 1500-1900 to give a comprehensive overview, but I can speak to a few things that might help. First, I would guess the European colonization of North and South America and the Atlantic Slave Trade of Africans were what gave Europeans the money and resources to make many of the technological achievements they did in this period. In contrast, African's were losing resources and people in this time period.
In regards to metallurgy, there is a long history of it in Sub Saharan Africa. In west Africa, it goes back as far as 1000 BCE in the Nok culture of ancient Nigeria. In later periods, the Yoruba, Edo (Bini/Benin), and Igbo made some of the finest metal sculptures in all the world before the industrial age (you should check them out if you are not already familiar). In ancient Sudan, iron smelting was a key part of the Kushites' economy, going back as far as 600 BCE. I've read one scholar saying that the proportional amount of iron production there was almost as high in Europe in the industrial age. There is also long history metallurgy in south east Africa, but I don't know enough to give any specifics about it.
In regards to abundant water, all the major pre modern African civilizations I can think of were coastal or along major rivers--such as the Nile, the Niger, and the Congo river--so I think you are right about it being important. In my last comment I mentioned how the medieval Malians and Somali both defeated the Portuguese in naval battles, and how the medieval Somali had a colony in the Maldives. Also, Abu Bakr II of Mali attempted to cross the Atlantic in the 14th century, but we don't know whether or not he made it across. The Habesha ethnic groups in the horn had control of parts of Arabia at various points in history, so I imagine they had good control of boating.
Another thing to important thing to discuss is that is that technological advancement usually comes about because there is a need for it, or at least a desire for it. Because of this, there were many peoples all over the world who were totally fine with how they were living until European colonists arrived. One interesting thing to bring up here is the relationship between Japan and Ethiopia in the late 19th and early 20th centuries. This is a topic I wish I knew more about, but even the basics are very significant and interesting. My understand is that the two nations saw themselves as highly similar, being two of the most advanced non-white nations at the time. The Ethiopians saw the rapid modernization of Japan and wanted to emulate it, but they were only somewhat sucessful. The Japanese people also had very favorable atitudes towards Ethiopia and Ethiopians, but in the Second Italo-Ethiopian War, when Haile Selassie was looking for allies, the Japanese government declined (they probably couldn't have done much for the Ethiopians even if they wanted to, I think). Some scholars say that the reason Europeans didn't colonize Japan and weren't as resistant to it's modernization was because of it's lack of resources. Africa, of course, had tons of economic value to Europe, so it's been more of a mix between exploiting Africa and helping Africa develop.
Did you know the word Africa means dry soil?
No, I've never heard that. I know there are more than a couple of proposed etymologies for the name "Africa."