A literal understanding will connect it with a "spare no expense" doctrine which prescribes the acquisition of the best state of the art technology available, without regard for traditional cost-benefit analysis.
"But no person shall be subject to the foregoing penalties for any act done in the exercise of any right to which he is by law entitled, if he prove to the satisfaction of the court, before whom he is tried, that he has used the best practicable means, within a reasonable cost, to render harmless the liquid or solid matter so permitted to flow or to be put into waters."
Best available techniques not entailing excessive costs (BATNEEC), sometimes referred to as best available technology, was introduced in 1984 into European Economic Community law with Directive 84/360/EEC.
[5] The BAT concept was first time used in the 1992 OSPAR Convention for the protection of the marine environment of the North-East Atlantic for all types of industrial installations (for instance, chemical plants).
Best available techniques not entailing excessive costs (BATNEEC), sometimes referred to as best available technology, was introduced in 1984 with Directive 84/360/EEC and applied to air pollution emissions from large industrial installations.
The Clean Water Act (CWA) requires issuance of national industrial wastewater discharge regulations (called "effluent guidelines"), which are based on BAT and several related standards.