Insert mandatory 'milking it' joke here. 

So this is Olivia Wilde - who recently sparked an always needed debate after partaking in a Glamour Magazine photo shoot depicting her breastfeeding her four-month-old son in a diner - dumping a pale of her own breast milk over her head for the Ice Bucket Challenge. She says it took her all night to make but, speaking from experience, that would take the average person about a week to pump, so she's clearly have a larf - fair play to her.  

One can only assume it's water a bit of whitewash mixed in. If it's milk - in any form - it's a bit wasteful *waggles finger while gingerly dismounting soapbox*