I Just remembered this - years ago when I adopted an outdoor kitty, he wouldn't drink his water, but would go to my roomate's cats' water.

She explained that because she used filtered water (Brita pitcher), it tasted more like water that an outdoor cat would drink. Puddles, etc.

I started using the filtered water and my cat was drinking it!

If you don't have a pitcher like that (there are generic ones that are less expensive), maybe borrow one or buy a bottle of water and see if that makes a difference.