barry peterson shows us state investigators want to know how thc wound up in the water well. >> when we have a presumptive positive of thc in our public water we take that extremely serious and we will investigate that until the even. >> reporter: police say substance may have been introduced in the system, at one of the town's five water wells, and if so, it looked like it was done on purpose. >> there were signs of tampered, forced entry if to what would have been the raw water supply. >> reporter: presence of thc was discovered by a company that conducts routine employee drug tests but the results, are far from definitive, and samples are on their way to state labs. still, it is cause for big concern in this small town of more than 700 people. >> i was in the grocery store, and i was in there about ten minutes and in that amount of time people had rushed in and sold out of the water. >> this causes real concern, because, if it happened to people in colorado, it can happen anyplace. >> reporter: colorado law permits the legal saying of medical and recreational marijuana but countie

barry peterson says the fbi is involved. >> when we have a presumptive positive of thc in our public water we take that seriously and we are going to investigate that until the end. >> reporter: police say the substance may have been introduced into the system at one of the town's five water wells. if so it was done on purpose. >> there were signs of tamper forced entry into what would have been the raw water supply. >> reporter: the presence of thc was discovered by a company that conduct routine employee drug tests. but the results are far from definitive. and samples are on the way to state labs. still, it's cause for big concern in this small town of more than 700 people. >> i was in the grocery store. i was in there about 10 minutes and in that amount of time, people bought all the water. >> this causes a real concern because if it happens in hugo, colorado it can happen anyplace. >> reporter: colorado law permits the legal sale of medical and recreational marijuana. but counties can decide whether or not to allow it. hugo part of lincoln county does not contain any commercial p