How can I include an item in the bom for weighing purposes if I don't want to consume it. For example we have water in the boms.

can you put it at minimal quantity, if you need the actual quantity then put it at minimal price

I don't want them to have to consume it on the floor.

hmmm maybe you can make it a service item or non inventory item so it doesn't get consumed

Yes create it as a non inventory item. Then you can give it attributes like an inventory item but they don't need to do anything on the WOI for it