Only with 3 different Spotify accounts.  

Thanks for the quick reply. 
 

do you know a music app that would allow this? Thanks again! 

I use Amazon Music and it allows multiple streams to a single Sonos system.  You mention “3 different Sonos systems” and later mention “3 different rooms”.  This is confusing.  Do you actually mean 3 different systems?  Because I don’t know of any singe service account that will stream simultaneously to different Sonos systems.  Most can stream to 3 different rooms on the same system, but not 3 separate systems.

Maybe I’m explaining it wrong. 
 

so, have 3x Sonos One products. 
each product, in a different room. 
and each room, playing different music at the same time. 
 

but using one music app to control all 3 if that’s even possible?

From the Sonos perspective, that is what it is designed for, three Sonos ‘rooms’ that can play up to 3 different things simultaneously. The issue is, however, often the streaming company, which may restrict the number of active streams. As ​@jgatie suggested, Spotify is one of these. But the restriction isn’t on Sonos’ side.

​@JoshG96 

If you subscribe to Spotify Family Classic (or any music streamer’s family tier), you can have multiple accounts. You can then add as many accounts to the Sonos app as you have number of speakers, and play music from a different account on each speaker simultaneously.

Edit- also everyone with an account under your family subscription can use Spotify Connect or Airplay to stream directly from their phone/device to their own speaker without affecting the other speakers.

You can do this with most services using one account.  I know Amazon Music and Apple Music has the ability to do multiple streams in more than one room.  Spotify’s rules are more strict.  They need an account to be added for each individual stream.  They can be Family accounts, or actual separate accounts.