In the v4_Outdoor Water Use Reduction Calculator, there is a tab where you need to key in the Monthly Rainfall and Evaportranspiration Rate (ETo) for the location of the project. 

I've been scouring the internet for the Evapotranspiration Rate of Singapore but for the life of me, I could not find it. Is there a way to compute the ETo based on other readily available climate/weather data for a given location?