The activated carbon in the filter will reduce amounts of organic compounds (like pesticides) and also chlorine. Because interactions are very complex, we cannot yet guarantee certain removal rates. Also, we have never found high levels of other chemicals in raw water and our contacts at the Ministry of Health and ITB also report that the only issues regarding drinking water are bacteria, iron & manganese, and sea water intrusion (high TDS) and humic-acids. Arsenic has been reported in a few deep wells in South Sumatera. However, according the ministry of health arsenic contamination is rare out site of mining areas. If people install a deep well, it is always recommended to do a full chemical test which is cheap compared to the costs of drilling such a well. If you are not sure about your well water, rain water is abundant in 90% of Indonesia.