A review of 35 outbreaks of cryptosporidiosis points to recommendations for prevention of waterborne outbreaks and uncovers a need for more adequate epidemiological data. Cryptosporidium parvum infection occurs worldwide in urban and rural populations, and waterborne outbreaks have been associated with consumption of contaminated drinking water and water during recreational activities. This article reviews the epidemiology and causes of waterborne outbreaks that have been reported in North America and the United Kingdom. Outbreaks were associated with filtered and unfiltered surface water sources, groundwater sources, and contamination of the distribution system. In most outbreaks, sources of contamination and deficiencies in treatment and operation were identified. Available epidemiological information is inadequate to estimate endemic waterborne risks, and analytical studies should be conducted to assess these risks. A major issue to consider in assessing waterborne cryptosporidiosis risks is the role of protective immunity, which may be acquired through low‐level sporadic exposures to C. parvum in drinking water.

Pilot-scale column experiments were conducted in this study using natural soil and river water from Ohio river to assess the removal of microbes of size ranging over 2 orders of magnitude, i.e., viruses (0.025-0.065 microm), bacteria (1-2 microm), and Cryptosporidium parvum oocysts (4-7 microm) under conditions representing normal operation and flood scour events. Among these different organisms, the bacterial indicators were transported over the longest distances and highest concentrations; whereas much greater retention was observed for smaller (i.e., viral indicators) and larger (i.e., Cryptosporidium parvum oocysts) microbes. These results are in qualitative agreement with colloid filtration theory (CFT) which predicts the least removal for micrometer size colloids, suggesting that the respective sizes of the organisms was a dominant control on their transport despite expected differences in their surface characteristics. Increased fluid velocity coupled with decreased ionic strength (representative of major flood events) decreased colloid retention, also in qualitative agreement with CFT. The retention of organisms occurred disproportionately near the source relative to the log-linear expectations of CFT, and this was true both in the presence and absence of a colmation zone, suggesting that microbial removal by the RBF system is not necessarily vulnerable to flood scour of the colmation zone.

Riverbank filtration (RBF) is a low‐cost water treatment/pretreatment technology that is used in many countries around the world for water supply. When wells are situated close to rivers or lakes and pumped, the surface water is induced to flow to these wells. During soil and aquifer passage, chemical, biological, and particulate contaminants are removed. Many European cities have been using RBF as the primary source of drinking water production for over a century. In the United States, RBF is gaining popularity owing to favorable regulatory provisions. In siting and designing RBF systems, the river hydrology and site hydrogeology must be carefully considered so that scouring and clogging are avoided and the aquifer is conductive to produce the desired amount of water. The source water should be of reasonably high quality to avoid the development of anoxic conditions, which ultimately may lead to the reduction of iron, manganese, and other redox‐sensitive species. Three‐dimensional computer models are increasingly being used for the placement and operation of RBF systems. The collection system can be vertical wells, horizontal collector wells, infiltration galleries, or combinations of any two or all three. Site‐specific conditions, pumping needs, and the availability of treatment plants for further treatment of the filtrate dictate the type of collection system. The capital cost is tied to the type of collection system, conveyance system, and land acquisition. Numerous studies have pointed out the benefits of RBF in removing turbidity, pathogens, dissolved chemicals, natural organics (which are regarded as precursors for disinfection by‐products for systems using chlorine as the disinfectant), and a whole host of micropollutants.

Prevention of waterborne disease outbreaks is a primary objective of drinking water treatment. As required by the Information Collection Rule (ICR), selected US water utilities have begun monitoring for specified chemical contaminants, Cryptosporidium, and other waterborne pathogens. When Cryptosporidium oocysts are detected during ICR monitoring, will these surveillance programs be able to estimate the risk of waterborne cryptosporidiosis? This article addresses such questions in a look at the future of surveillance programs for waterborne disease.