Best urban water management practices to prevent waterborne infectious diseases under current and future scenarios

Water in urban areas may pose a public health risk when people are exposed to urban water, because it may contain pathogens. These pathogens may originate from fecal bird droppings, runoff from paved surfaces (including e.g. dog feces), growth of micro-organisms in water and in some cases discharges of combined sewer overflows. Since the extent to which exposure to urban water poses a risk for public health was unknown, this thesis aimed to investigate health risks associated with urban water systems and to determine ways to minimize those risks. Chapter 1 provides an overview of pathogens that have caused outbreaks of waterborne illness. (The lack of ) Water quality guidelines, regulations and policies for urban water management are also addressed. Exposure to contaminated aerosols and water originating from water features may pose public health risks. In chapter 2, endotoxins (in air and water) and fecal bacteria (in water) of water features were measured as markers for exposure to microbial cell debris and enteric pathogens. Exposure to air and water near water features was shown to result in exposure to endotoxins and fecal bacteria, which may lead to respiratory health effects and gastrointestinal health complaints. Regression analyses showed that the endotoxin concentration in air was significantly influenced by the concentration of endotoxin in water, the distance to the water feature and the tangibility of water spray. This study provides estimates for aerosolisation ratios that were used as input for a quantitative microbial risk assessment in chapter 3 to quantify infection risks for exposure to splash parks. In the Netherlands, rainwater becomes more and more popular as an economic and environmentally sustainable water source for splash parks.The associated public health risk, however, and underlying risk factors were unknown. Therefore, in chapter 3, a quantitative microbial risk assessment was performed using Legionella pneumophila as a target pathogen to quantify the risk of infection for exposure due to inhalation and Campylobacter jejuni by ingestion. The risk of infection for a mean exposure duration of 3.5 minutes was 9.3*10-5 for inhalation of L. pneumophila and 3.6*10-2 for ingestion of C. jejuni. The results of the QMRA showed that using rainwater as source water for splash parks may pose a health risk. This study provided a methodology to quantify exposure volumes using observations on site. Furthermore, it gives insight into the effect of setting water quality standards, which may limit infection risks from exposure at splash parks. Splash parks have been associated with infectious disease outbreaks as a result of human exposure to poor water quality. To be able to protect public health, in chapter 4, risk factors were identified that determine poor water quality. Samples were taken at seven splash parks and were analyzed for E.coli. Higher concentrations of E. coli were measured in water of splash parks filled with rainwater or surface water as compared with sites filled with tap water. Inspection intervals and employed disinfection has no significant additional effect on the fecal contamination of the water. Management practices to prevent fecal contamination and guarantee maintaining good water quality at splash parks should include selection of acceptable source water quality and application of disinfection Flooding and heavy rainfall have been associated with waterborne infectious disease outbreaks. It is unclear to which extent they pose a risk for public health upon exposure. In chapter 5, risks of infection from exposure to urban floodwater were assessed using quantitative microbial risk assessment. To that aim, urban flood waters were sampled in the Netherlands. The water contained Campylobacter jejuni, Giardia spp., Cryptosporidium spp.,noroviruses and enteroviruses. Exposure data were collected at flood sites by questionnaires. The mean risk of infection for children who were exposed to floodwater originating from combined sewers, storm sewers and rainfall generated surface runoff was 33%, 23% and 3.5% per event, respectively, and for adults it was 3.9%, 0.58% and 0.039% per event. Warm, wet weather has been associated with cases of Legionellosis, the source of the majority of the infections, however, remains unknown. Therefore, in chapter 6, urban waters and water of wastewater treatment plants were analyzed for Legionella. Legionella was present in 3 of 6 samples of urban floodwater originating from rainfall generated surface runoff and in 5 of 24 samples originating from wastewater treatment plants. Several isolated Legionella strains belonged to sequence types that have been previously identified in patients. The presence of Legionella in urban floodwater indicates a possible transmission route for this pathogen. In chapter 7 the results of the study are discussed. The risks of infection from exposure to splash parks and floodwater were compared with the risk of infection after swimming in bathing water of good water quality according to the European Bathing Water Directive. This comparison showed that the risk of infection per case of exposure was higher for exposure to floodwater and splash parks than for swimming. The yearly infection risks are, however, dependent on the presence of pathogens in water and the frequency and the extent of exposure per year. Furthermore, new scenario’s for urban water management, like climate change and new sanitation, which may change the health risks associated with urban watermanagement were discussed. Subsequently, recommendations for the prevention of health risks associated with water features, splash parks and urban floodwater were discussed.