EPA recently announced they are moving forward, contrary to the policy of the Bush Administration, with setting standards for various toxics in drinking water. Unfortunately, attention is not being given to a serious health threat, amoebas in drinking water.
Amoebas (see http://en.wikipedia.org/wiki/Amoeba_(genus)) can trigger disease, from a blinding corneal infection to a rapidly lethal brain inflammation. They also carry bacteria, which allows the bacteria to not only multiply inside the amoeba, but also to evade disinfectants. Yet, amoebas are considered an unquantified emerging health risk in drinking water, and facilities are not required to screen for them. Researchers recently analyzed data from 26 studies in 18 countries; all found amoebas in drinking water systems, and nearly half found amoebas in tap water. Other researchers found amoebas in many U.S. surface waters, and nearly half of the post-treatment water from drinking water facilities still had amoebas present.
Water treatment does reduce substantially the number of amoebas in drinking water, but not all systems work perfectly all the time. Studies in Florida found 1/5 of home water had amoebas; the authors speculated that either they escaped the treatment system, or entered water pipes through cracks and other imperfections.
Lab research indicates that chlorea outbreaks are more likely when associated with amoebas. Researchers believe the bacteria multiple inside the amoebas so that upon ingestion a human receives a substantial dose of bacteria.
For further information on this topic, see http://aem.asm.org/cgi/content/abstract/69/10/5864, http://www.iwaponline.com/jwh/006/jwh0060099.htm, http://www.iwaponline.com/jwh/006/jwh0060209.htm, http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WFH-4XCYJG9-1&_user=10&_coverDate=09%2F30%2F2010&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1630822874&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=5d223edc57524b10d3f1f5cd51de78de&searchtype=a, and http://pubs.acs.org/doi/abs/10.1021/es102876y.