In theory, any molecule of any substance that is not a water molecule can be defined as a water pollutant. Some substances, such as minerals, are actually beneficial in some quantities because they give the water a pleasing taste or have a positive health effect. Others, such as carcinogenic organic compounds, are harmful in any amount and should be removed at all costs. Not all are harmful, but many cause water-quality problems more frequently than any other pollutant. Dissovled solids are solid materials like fluoride, nitrates, sulfates, and salts, which decompose in water.
Radioactive particles are minute bits of radioactive materials.
The first step is to find out which of these pollutants might be in your water and which you want to remove. If your water supply is regulated by the Safe Drinking Water Act, call city halls, your local water district, and your local department of health services to see if they have recent test results for the pollutants they require to be monitored. One limitation to the water-quality data that come from your local waterworks is that the reports will tell you the quality of the water as it leaves the treatment plant, not as it comes out of your tap . The levels of chlorine, metals, bacteria, and particulates may have changed by the time the water is pumped through the distribution system to your home. Ask these laboratories what testing they do and get estimates from several, because prices and services can vary.