Without a doubt, one of the more pressing environmental challenges deals with the issue of sewage treatment. This is because, as noted by the National Center for Policy Analysis, sewage systems in some 770 cities are outdated, with many having been built more than a century ago. Thus to meet new clean water standards, many communities – which have in the past simply dumped untreated waste into rivers during heavy rainfall – must now build new facilities or massive underground tanks to hold their sewage, and the costs for this are simply extravagant. Since the federal government once subsidized some 95 percent of this cost, but today only covers about 5 percent, sewage treatment is one issue likely to get even more icky.