To help students understand that clear water isn't necessarily free of pollutants, place 5 clear liquids in portion cups. Things to include should have a definite taste that students would recognize. Use sugar water, white vinegar, salt water, water mixed with citric acid, and tap water. After students have all had a chance to taste, discuss that some kinds of pollution can't be seen. If you have local creeks, streams, or other water ways that are unsafe for human use, this is a good jumping off point to discuss the problems these bodies of water have.
All resources are available in most areas.
Environment concerns can be understood by even the youngest school children. Providing them with a background of information and an opportunity to actively use that information, they will begin to develop a feeling of stewardship for their world. Using activities that develop environmental stewardship in students will hopefully become a basis for action in their future lives.