Under current federal law, public water supplies that serve fewer than 10,000 people are not required to monitor or control trihalomethanes (THMs). Small water utilities in Iowa were surveyed to determine whether THM contamination is a problem and to identify measures for THM control appropriate for small utilities. Grab samples were collected in July and August 1983 and September 1984 from treatment facilities and from distribution systems in communities with fewer than 10,000 residents. More than 75 percent of the communities had THM levels in excess of the maximum contaminant level. Treatment modifications that influence the formation of THMs are reviewed and control measures appropriate for small utilities are recommended. Includes 18 references, tables, figures.