Follow
“sund”= a narrow area of water between two areas of land that connects two lakes for example
“ström” = “stream”
“Sundström” is not as one may think a compound noun, that is, it consists of two words “sund” and “ström”, but combining the two words together do not form a new word. So, actually, this name does not "mean" anything in Swedish.
“Sundström” is from the beginning/middle of 1500. It was common during that time that when the craftsmen finished their training they took on a name that had something to do with their profession. These names where always inspired by nature:
Ek/man (oak/man)
Fors/lund (rapids/grove)
Perhaps “Sundström” was a “rafter”?