I have a plastic heated pet bowl similar to this: http://www.tractorsupply.com/tsc/produc … _vc=-10005 I was wondering if I could fill it with sand instead of water so that my hens have a place to dust bathe inside the coop on days when it's really cold and windy - like today. It was -30 C, with winds gusting to 38 km/h from the NW at 7:00 a.m. Does the pet bowl have to contain water? Will the plastic melt if I fill it with a non-liquid? The bag of sand I have is stored outside and is rock solid because it's got quite a bit of moisture in it, but I plan to bring it in to thaw if I can use it safely in the pet bowl.