Authorities say it looks like vandalism, not terrorism, CBS Boston reported.
The incident occurred at the Hultman Aqueduct in Framingham, which is one of the two lines that carry drinking water to metro Boston area.
CBS Boston reported the three padlocks were cut from separate access hatches located at approximately half-mile intervals along the aqueduct. Police say there is evidence of an attempt to cut a fourth lock.
State police are investigating, though they say "there is no evidence of any crime other than vandalism."
The Massachusetts Water Resources Authority says it doesn't appear anyone tried to tamper with the water supply and there does not appear to be any contamination or changes in water quality.
According to CBS Boston, last month, authorities stepped up patrols at public water supplies after seven people were caught trespassing at the Quabbin Reservoir in Belchertown, Mass.