Question: I read in an American Accent book that there is no break between sibilants adjoining each other between words. For example, this phrase:

> 
> I was starting to worry.
> 
> 
> 

The words *was* + *starting* sound like [wə**zs**tɑrt̬ɪŋ] with no break. Am I right? I marked the sibilant sounds with bold.

I used the schwa sound in *was* because it's a function word and we usually give stress to content words and reduce the function words. I also used the tapped T in the word started.

Answer: 
Well, there is never a break between words unless you make one. You could say first the word "was", stop making sounds, then say "starting", if you chose to make that break. If there is no period of silence between them, the [zs] pronunciation is just a [z] followed immediately by [s].

If you happen to be an English speaker who customarily devoices word-final obstruents, like /z/, then the last sound of "was" will be voiceless, but it would have been anyway, regardless of whether "starting" followed. Details of how exactly word final /z/ is pronounced in various English dialects are interesting in themselves, but so far as I know, they have nothing to do with whether the next word starts with /s/.
You are right. Was, despite ending with an 's' sounds like a 'z' with an American speaker no mater where you are. Because of that [wəstɑrt̬ɪŋ] isn't correct. That would only work if both the 's' in "was" and "starting" were pronounced the same. As for the lack of break, that would be correct as well. Even in a lengthened cadence such as in a Texan Drawl, it is really hard to separate them out into two distinct words and have it sound right.