Read the following passage and answer the item that follows. Your answer to this item should be based on the passage only.

The colour that leaves a dyeing unit does not stay in the river long, and that is part of the problem, because by the time anyone samples the water the visible sign has gone while the salt load and the spent chemistry have not. Downstream wells in dyeing clusters have turned brackish, and fields watered from them have gone out of production. Common treatment plants were built for several of these clusters and many now run under capacity or not at all, because sending effluent to them costs a unit money that discharging into the drain does not.

Which one of the following statements best reflects the most logical and practical message conveyed by the passage?