Oh, I'm sure the kitties love that drink - mine would love it, too - but you should really consider to make them get used to water. Like others have said, cats are usually lactose-intolerant, and the lactose of cow milk may cause diarrhea, or at least a sore tummy.

This is from an article I wrote some years ago for my cat website:

... "But many cats don't tolerate cow milk very well, they're getting diarrhea from drinking it. This is because cow milk contains more lactose (milk sugar) than the cat mother's milk. The organism of an adult cat is lacking the enzyme lactase which breaks down the milk sugar - and this leads to cow milk intolerance. The cat mother's milk, on the other hand, contains more fat and different proteins, so the composition of both cow milk and cat milk cannot be compared." ...

The entire article is here: Milk & Cats

I think when your cats are able to tolerate this drink, you may still want to offer it to them as a treat, but their daily drink should be water.

Kirsten