Increase in stock

Dear Experts,

We are implementing for Dairy and here they procure milk and kept in several SILO, at the end of the day they wash SILO with water, but all water is not drained off, so some up to 2-3 thousand liter water remains, and next day when they again load milk in that so water plus milk that stock gets increased, they having a report in which they show that the milk stock is increased due to water, but how should we map this in SAP.

Thanks & Regards,

Karad D D