You might not think much about where the water in your tap comes from. Is it from a municipal source or from a private well? How is the quality of the water? You should be receiving updates from the city where you live if you are connected to the municipal water system. These might seem a little overwhelming at first, but usually they will highlight anything that is out of order.
If you have a private well on the other hand, the responsibility for your water quality rests on you. There are kits to do tests for yourself, but it is better to send a water sample to a lab for testing, both for accuracy and a wider range of tests. You can find out acceptable levels of pollutants from the EPA (Environmental Protection Agency). Some chemicals might be safe at a low level for a short while, but many times they will build up in your system if the problem is not remedied.