I used white cranberry juice at first, not the cranberry cocktail. Then I got cranmax pills much easier and when she dripped all over the floor after drinking her water with the cran mixed in it, it got everything sticky. So cranmax pills much better way to go, some dogs may not like the sweet or the tart taste, depending on which one you get, I don't like adding alot of sugar, hence the pills, you may be able to find them at a health food store or find it on line
http://www.cranmax.com/
the other thing is the filtered water like a britta water pitcher or something liike it to get alot of junk out of the water.
Give a little bit at a time and see how they handle it, it may upset tummy if given too much or on empty stomach, but mine is okay with 500 mg a day, she's about 80 lbs. Someone once told me that they can't really overdose on it, it's just like drinking a bunch of cranberry juice, you pee it out. Same for ester-c vitamin she gets a pill a day, 500 mg. She has been clear for over a year. I try and make sure she drinks more water, so she flushes her system regularly.