The way I understand it is...it is strictly a ratio...
from tabasco.com
So how did Scoville discover these heat levels? His method was simple. He soaked each different variety of pepper separately in alcohol overnight. Because capsaicin is soluble in alcohol, the soaking extracted the pungent chemicals from the pod. Then Scoville took any measure of the extract and added sweetened water in incremental portions until he detected a level of heat on his tongue. For example, in the case of Japan chiles, it took sweetened water in volumes between 20,000 to 30,000 times the pepper extract before the heat level was not noticeable. He thus rated the Japan chiles 20,000 to 30,000 Scoville Heat Units.
to me, this means that if you have 1 ml of the sauce/pepper/whatever and it is rated at 357K SHU, it will take 357,000 ml of water before you can't taste the heat....