A water trough is basically a big bucket full of water. Except, it's actually a lot larger than your standard sized bucket. A regulation size water trough can be anywhere from about three feet long, one foot wide and two or so deep, to a much larger, three foot deep, ten feet in diameter cylindrical basin. Water troughs can be made from plastic, wood, metal, and anything else that can be fashioned into a form that can hold a liquid at room temperature. But not really cold helium, that stuff can climb out of water troughs.
Some water troughs have an insulating cover on them to help keep the water from freezing in the cold Canadian winters. Other have more ingeneious methods of keeping the water from freezing, and those near power lines will sometimes employ a heater, as in a heating element on a float, to keep the water in drinkable form. Some troughs don't have any fancy insulation or anything, and require human assistance to keep the stuff of life flowing.
If you want to find out more about the fascinating subject of water troughs, visit your local UFA or farm supply store.