Given that the maximum contaminant level of copper in potable water according to the Environmental Protection Agency (EPA) is 0.0013g/L
That means 0.0013 g of Copper can be present in 1 L water.
ppm(parts per million) is equivalent to the concentration of mg/L
1 ppm = 1 mg/L
We can convert 0.0013 g/L to mg/L in order to get the concentration in ppm.
Converting 0.0013 g/L to mg/L:

1.3 mg/L = 1.3 ppm
Therefore, 0.0013g/L can be expressed as 1.3 ppm