Validation of WaterGEMS modeling outputs/result

Hello Everyone,

I am using WaterGEMS for a part of my research work. In a recent presentation of my work, the audience had a lot of questions on the authenticity of the results obtained using WaterGEMS. Unlike, in EPANET the codes are not in open source for WaterGEMS. Their query was, if there is any document/paper vouching for the modeling capabilities of WaterGEMS. If any such document is available, I should refer to it in my work. It was also mentioned that in other water research field, the commercial software results are validated with that of other softwares with known codes. Due to my lack of experience, I could not convince the audience with my answers.

Hence, I would like to know how to tackle such questions from people working in different research fields in future. 

Thanks a lot in advance.