Two of my friends have 4 year old mid sized dogs that have developed cancer. It turns out both dogs have been drinking and eating from fairly new stainless steel dog bowls made in China. When the bowls are filled with clean water an oily film forms on the water surface. A large veterinary service in the area has compiled info relative to these pet bowls and cancer in pets. We speculate the film may be from the SS manufacturing process in China. If you see this film on clean water in your pets SS bowls, stop using it. With any pet bowl, I'd run it through an automatic dishwasher on sanitize setting before using. Spread this around to fellow pet owners.