I've Watched Way Too Much Science Channel

Its been on while I've been doing random other things. And now there are a bunch of episodes of "How Its Made" where I've seen all the pieces.

But I haven't been paying quite enough attention to figure out if episodes always have the same contents. For example the current episode ends with racing wheelchairs and parquetry. Which I know I've "seen". But it starts with train rails and desalinated water, which I don't remember seeing...