Which one of the following statements is not true?

• Correct answer
  A

  Concentration of DO below $6 \mathrm{ppm}$ is good for the growth of fish
• B

  Clean water would have a BOD value of less than $5 \mathrm{ppm}$
• C

  Oxides of sulphur, nitrogen and carbon are the most widespread air pollutant
• D

  $\mathrm{pH}$ of drinking water should be between $5.5-9.5$

Hence, the correct answer is option: 'A'.