污染源的质量越高，微生物和化学污染物的风险越低。如今，可以利用技术处理任何质量的水，从而将污染物浓度降低到几乎任何所需的水平。然而，除了在非常特殊的情况下，对于社区来说，成本太高，与该技术的运行和维护相关的人类弱点可能会对人类健康造成严重影响。可以毫不矛盾地说，面对隐孢子虫等微生物污染物，这些污染物不容易监测、灭活或清除，而且认识到在许多发展中国家，监测和预防老年腹泻病仍然不是很有效，需要更多地注意选择可用的最佳水源，并通过对流域的土地使用控制和卫生措施保护这些水源。 我们的担忧与150年前困扰我们祖先的担忧相似；预防感染性水传播肠道疾病。

The higher the quality of the source, the lower the risk from both microbial and chemical contaminants. Technology is available today to treat water of any quality so as to reduce the concentration of contaminants to virtually any desired level. However, except in very special situations, the costs are far too high for communities and the human frailties associated with operation and maintenance of that technology can result in serious impacts on human health. What can be said without contradiction is that, in the face of microbial contaminants such as Cryptosporidium, which are not readily monitored, inactivated or removed, and in recognition that monitoring and protection against the older diarrheal diseases is still not yet very effective in many developing countries, much more attention needs to be given to selection of the best sources available and protection of those sources through land use controls and sanitation measures on the watersheds. Our concerns have become similar to those which troubled our forebears 150 years ago; protection against infectious waterborne enteric disease.