The potential impacts of exposure to various contaminants in drinking water on cancer incidence have been investigated. This study was an ecological investigation as a follow-up to a previous study that looked at incidence rates and time trends of cancer by source of drinking water and size of municipality in Iowa. Cancer incidence ratios for the 16 most common cancers in Iowa were analyzed by size of municipality, by source of drinking water, and by well depth and aquifer for groundwater sources. Time trends were also evaluated. The following results were found: 1) Male and female lung cancers increased as size of community population increased; 2) There is a significantly higher incidence of female lung cancer in towns population 1,000-10,000 using surface water; 3) For communities using groundwater as their source of drinking water, the study found higher rates of lung cancer and total cancers in females in towns with shallow wells compared to towns using deep wells; and 4) Findings show a significant increase in trend over time for lung cancer in both sexes, regardless of water source or well depth, and show a significant increase in the incidence of male bladder cancer in towns with shallow wells, as well as a significant decease in the incidence of several other types of cancer in groundwater communities at various well depths. This study did not support all the findings of previous studies. In the future, this type of analysis will be conducted on a periodic basis, to continue the mission of CHEEC. Technical Report Available.