Jersey's water quality hasn't improved in the last year, according to latest tests.
Levels of potentially harmful nitrates in untreated water supplies are among the highest in Europe.
Although, they are still below health based limits.
Banned fungicide Oxadixyl was found to be at similar levels to last year, along with three other chemicals used in farming.
Farmers are being told to be vigilant as sudden rainfall can wash chemicals off the ground and into water.
The States has been working with an environmental group to tackle the problem.
Last week they trialled a machine which reduces the amount of fertiliser potato farmers use.