This was what we did with old bed sheets. Also, we use 3 gallon buckets they give us free from the bakery that frosting and garlic spread come in. You fill that up half full of water, freeze it overnight, and fill to the top with fresh water in the a.m. It lasts most all day with a huge floating iceberg in it until very late in the afternoon. And if you wait till noon to put that out, it may still have ice in it at roost time, if it's in shade like under this bed sheet "tent".
That bucket sits into a hole dug for it so it's partially below ground, which helps the ice stay frozen longer.

That bucket sits into a hole dug for it so it's partially below ground, which helps the ice stay frozen longer.