Water supplies in one US town have been tainted with THC, the active ingredient in marijuana.

Police in the Colorado town of Hugo say there is evidence of forced entry and tampering at one of the town’s water wells.

Tests of Hugo’s tap water revealed the presence of THC, or tetrahydrocannabinol, the active chemical in marijuana, which is linked to psychological effects including increased humour and appreciation of Jimi Hendrix.

These results came from a quick field test, but samples have been sent for deeper analysis by the Sheriff's Office.

The contamination was initially revealed by a local company using the field tests to check employees for drugs, but had in this case tested tap water.

The quantity and potential risks of the THC in the water are not yet known, but because the chemical does not easily dissolve in water, experts say there is a low chance of achieving a high.

The damaged well has been sealed, and the town's water lines are being flushed out, so it should be safe to drink again within days.

The water is considered safe for washing hands, dishes, laundry, general cleaning and brushing teeth.

Free distribution of bottled water has begun, with each of Hugo’s 720 residents given four bottles.