What exactly is coconut water and is it available in super markets?

coconut water is the juice inside the coconut. you can buy pure coconut water as a drink - use that. if you can't get it, use water. You would need to use sweet condensed milk to make this ice cream, its what makes it churn free too.

Coconut water is the clear liquid inside of coconuts. I see it in grocery stores everywhere in the United States, as it has been quite popular here as a drink for the past few years (or longer). Check the ingredient list, though, to see what is actually in the product. There could be additives, including sugar, depending on the manufacturer.

And to answer your question about the condensed milk, yes, given that there is no other sweetener in the ingredient list for this recipe for pandan ice cream, I would have to conclude that sweetened condensed milk is intended. ;o)