Which statement accurately describes mg/L in relation to ppm for water?

Which statement accurately describes mg/L in relation to ppm for water?

• A. 1 mg/L equals 100 ppm
• B. 1 mg/L equals 0.01 ppm
• C. 1 mg/L equals one ppm
• D. 1 mg/L equals 1 ppb

Answer: (C)

In water, mg/L is effectively the same as ppm because ppm is a mass-based ratio and 1 liter of water has a mass of about 1,000,000 mg. So 1 mg of solute in 1 liter of water is 1 part per 1,000,000 parts water, i.e., 1 ppm. That makes 1 mg/L equal to one ppm. The other options would imply different ratios: 1 mg/L would not be 100 ppm or 0.01 ppm, and 1 mg/L is far from 1 ppb (which is 0.001 mg/L or 1,000 ppb in 1 mg/L).

In water, mg/L is effectively the same as ppm because ppm is a mass-based ratio and 1 liter of water has a mass of about 1,000,000 mg. So 1 mg of solute in 1 liter of water is 1 part per 1,000,000 parts water, i.e., 1 ppm. That makes 1 mg/L equal to one ppm.

The other options would imply different ratios: 1 mg/L would not be 100 ppm or 0.01 ppm, and 1 mg/L is far from 1 ppb (which is 0.001 mg/L or 1,000 ppb in 1 mg/L).