The standard applies to all types of water. The detection limit depends on the device used; In general, nickel contents can be determined from 0.02 mg/l. For nickel levels lower than 0.1 mg/l, an extraction method is recommended, see 10.
NEN 6456-1981 history
1981NEN 6456-1981 Water - Determination of nickel content by atomic absorption spectrometry (flame technique)