In the exercise of their functions under this Act and the Act of 1949 it shall be the duty of F1Natural England F2, the F3NRBW , the Forestry F4Agency and local authorities to have due regard to the protection against pollution of any water, whether on the surface or underground, which F5belongs to the Environment Agency, the NRBW or a water undertaker or which the Agency, the NRBW or a water undertaker is for the time being authorised to take.