Farmers could face "enforcement action" if they abstract water without the necessary licence or in breach of conditions, the Environment Agency has warned.
Farm inspectors are uncovering widespread unlicensed water abstraction in Devon and Cornwall during routine inspections, according to the agency.
Over the past two years, inspectors have taken 70 enforcement actions, requiring farmers to install meters to track water usage and apply for licences where needed.
Many farms depend on private water sources such as springs, wells, and boreholes, but the volume of water being drawn is often unmonitored.
The Environment Agency says this raises the risk that farmers may unknowingly exceed legal abstraction limits without a licence.
Lisa Best, agriculture team leader for the agency in Devon and Cornwall, said: "All landowners should know how much water they are abstracting and ensure they have the relevant licence if needed.
"Abstracting water without the necessary licence or in breach of your licence conditions is an offence and could lead to enforcement action.
"Taking 20,000 litres of water a day is enough to wash over 100 cars. Taking more water than you are permitted could impact on other users and damage the environment."
The agency regulates how much water can be taken through a licensing system: anyone abstracting 20 cubic metres or more per day must hold a licence.
Abstraction licences include conditions to protect the environment and the rights of other water users.
The agency has the authority to manage water use under existing licences, decide on new applications, and amend or revoke licences if abstraction harms the environment.
