Petro-proof plastics will often not pass tests to be used in food/water applications. They leach tiny amounts of chemical which can be tasted (a good test when no one can say what a good mineral/salf level is) in water and so rejected. Put water in a petrol can for 6 months in bright sunlight and you'll probably increase your risk of getting cancer by the same as smoking half a woodbine but no one really knows, the water standards have saved many lives in their time. Drink this water every day and you might have a reason to get a lawyer, hence they mark it. I have the same issue with pumps at work, no water standard markings if even perfectly safe, microscopic bits of rubber change the taste.