Humans use automobiles or buses as vehicles for travel. Similarly, disease agents can travel in vehicles—water, milk or even food. This is often referred to as vehicle transmission. Milk, so good for growing children, may be a disease carrier if it comes from a dirty or infected animal, which is why, in Western lands, milk must be pasteurized. Many people prefer to boil milk if there is any doubt about it. Food can carry sickness if prepared by unwashed hands or if it has been in contact with rodents or insects. But maybe the most commonly contaminated material is water. We cannot live more than four or five days without it, but if our drinking water is contaminated, it will be a vehicle of entry into our body for countless millions of disease agents. So, what disease agents can travel in water - bacteria, protozoa, worms, viruses and nonmicrobic poisons.