Proses oksidasi senyawa organik selama proses ozonisasi merupakan faktor utama meningkatnya kadar formaldehid di dalam air minum. Menurut IPCS dan IARC konsentrasi formaldehid di dalam air minum diharapkan kurang dari 100 μg/L. Sedang menurut Keputusan Menteri Kesehatan (Kepmenkes) RI Nomor 907/Menkes/SK/VII/2002 tentang Syarat-Syarat dan Pengawasan Kualitas Air Minum, kadar maksimum yang diperbolehkan adalah sebesar 900 μg/L. Untuk itu perlu dilakukan pemeriksaan adanya formaldehid dalam air minum dalam kemasan. Penetapan kadar dilakukan dengan metode kolorimetri menggunakan pereaksi Nash. Panjang gelombang analisis adalah 412,40 nm dan pengukuran serapan warna yang terbentuk maksimum 20 menit setelah tahap mereaksikan selesai. Dari 5 sampel yang diperiksa, 1 diantaranya positif mengandung formaldehid dengan kadar antara 50 - 67 μg/L Kadar yang terdapat di dalam sampel tidak melebihi batas maksimum yang diperbolehkan.Formaldehyde in drinking water arises mainly from the oxidation of natural organic matter during ozonation. According to IPCS and IARC concentrations of formaldehyde in drinking-water are expected to be less than 100 μg/L. And according to Republic of Indonesia Minister of Health Regulation Number 907/Menkes/SK/VII/2002 about Drinking Water Quality Observation and Conditions, concentrations of formaldehyde in drinkingwater are expected to be less than 900 μg/L. Therefore, a research for determine formaldehyde in bottled and packaged drinking water is necessary to be done. The level of formaldehyde can be determined with colorimetric method using Nash reagent. The maximum wave length analysis is 412,40 nm and measure the color that was showed maximum 20 minutes after the reaction's step was finished. The result of inspection from 5 samples, 1 sample shows contain formaldehyde on level of 50 μg/L - 67μg/L. In conclusion the level of the content within the sample didn't exceed the maximum in drinking water.