regression with covariate

#1
I want to develop a relationship between water temperature released at a dam and the volume of water stored in the reservoir behind the dam. But I need to factor out air temperature as both air temperature and the volume of water stored effect the temperature of released water. Any ideas on the best way to do this would be appreciated.
 

fed1

TS Contributor
#2
I humbly submit the following model:

water temperature = b1 volume + b2 air temperature + b3 volume*air temperature.

This is simple multiple regression model. Flexible enough for a man, but made for a woman.