Leaving DS with granny for whole afternoon for first time (wah!). He doesn't normally have breastmilk in the afternoon (5.5mo, on solids for few weeks. BF on demand as and when he feels like it, but this is generally just at mealtimes during day) but thought I would express a feed just in case. My boobs had other ideas and only managed to get about 3ozs! Can I add a little cooled boiled water to it so there is a wee bit more (say up to 5ozs)?