I am writing a book about an engineering subject but nothing very technical, just introductory to middle level. I made a bibliography section at the end of the book. There are also several sources, such as organization or government websites, from where I took only a statistical figure for example and I mentioned that source right there in the text. I didn't use them anywhere else. Do I need to include them also in the bibliography?
I think it would be better. Websites change, and so it is good practice to include the date you accessed it. It is also good practice to say who wrote or compiled it and the year it was published. And if you are including that information, it will be rather a lot to put in the middle of the text.
So it is best to include them in the bibliography, yes. Alternatively maybe you could put the information in footnotes.
If it is a normal published book, the publisher will have a policy about this, so it is up to them.