I am a working Mom... the precious breastmilk I so diligently pump is just the right amount for my 5 mo. DS to drink at daycare, so as I'm introducing cereal w/ a spoon, do i need to mix it with EBM? I've never supplemented, so would it be silly to mix with formula? Or should I just use bottled water if I don't have enough extra EBM? TIA!