THE TREATMENT OF RAINWATER FOR POTABLE USE

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1 THE TREATMENT OF RAINWATER FOR POTABLE USE C. Nash 1 1 General Manager, Sales & Marketing, Davey Water Products, cnash@davey.com.au Abstract This paper explores the development and application of water treatment systems for rainwater. Rainwater has been traditionally used as household potable water in rural Australian and New Zealand. Individual householders have been responsible for their own water quality and this paper explores the various treatment options currently employed in rural markets to ensure potable water. Some of the potential threats to human health from rainwater and subsequent treatment solutions are discussed. The use of rainwater tanks has now rapidly spread from Rural to Metropolitan homes in Australia due to water shortages in our major cities. This paper looks at the current non potable usages of this metropolitan rainwater. Future trends towards using the water for potable purposes in metropolitan Australia and potential treatment options are also discussed. Introduction A significant number of Australians and New Zealanders use rainwater for their drinking and general household water. The Australian CRC for Water Quality and Treatment (Occasional Paper 10) report surveys have shown that about 11% of Australians use rainwater as their main source of potable water. They report that rates of rainwater consumption in capital cities are lower than in regional and rural areas, with only 3.2% of capital city residents reporting rainwater as their main drinking water source, compared to 24.3% for other regions. They report the prevalence of rainwater consumption is notably higher in Adelaide (12.6%) than in other capital cities. This is no doubt due to the relatively poor taste caused by the higher salinity Adelaide s municipal water supply. The author estimates that approx 200,000 households in New Zealand use rainwater as their main source of drinking water. In both Australia and New Zealand the rainwater is typically run directly from a house and/or shed roof via open guttering into large, covered above ground water tanks. It is common to have from 20,000 to 100,000 liters storage of rainwater. The rainwater is pressurized and reticulated through the household via a small pump incorporating a sensing switch to detect water demand. Historically rural households would not have considered water treatment and disinfection of the rainwater. Rainwater has been considered to be safe and pure by most rural households. In some respects this is a reasonable assumption for the householder. The water falls from the sky onto the roof and into the tank. A simple process. Direct use of rainwater doesn t suffer from the age old problem of remotely supplied reticulated water sources potentially arriving at the household with the chance of contamination en route (by humans, animal or environmental).the householder using rainwater has the perception of direct control of the sourcing and purity of the water. In addition there has been no direct linking mechanism of illness and disease with the consumption of rainwater. In the past, episodes of gastrointestinal illness would have gone largely unreported and often not be linked to the rainwater consumption. It is only in the past few

2 years that doctors in Australia and New Zealand have had mandatory reporting of potentially water borne illnesses. Because consumption of rainwater has been a private activity the municipal water authorities and government health authorities have not had any involvement in measuring its quality and studying illness and disease episodes. Health Aspects of drinking Rainwater The consensus position among Australian and New Zealand health authorities is that well maintained rainwater collection systems can provide an acceptable potable water supply in situations where a disinfected reticulated supply is not available. In situations where a disinfected reticulated water supply is available, such a supply is preferable for potable use as the disinfected supply will have more reliable microbiological water quality than a rainwater tank supply. Potential health risks from ingestion of water from rainwater tanks relate to microbiological or chemical contaminants in the water. Microbial pathogens may originate from faecal contamination by birds, mammals, reptiles and amphibians that have access to roof surfaces or tanks. Studies of microbiological water quality have shown that faecal indicator organisms are often present in collected rainwater, and specific pathogens including Salmonella, Campylobacter, Cryptosporidium and Giardia have been detected. However, the absence of contamination from human faeces and farm animals means that the range of pathogens in collected rainwater is more restricted than that found in contaminated surface waters. Human enteric viruses (which replicate only in humans) should be absent from rainwater, and strains of Cryptosporidium and Giardia carried by animals with access to rooftops are likely to exhibit lower human infectivity than those from humans, cattle or sheep. For these reasons the risk of illness from consuming undisinfected rainwater is probably lower than for undisinfected surface water of apparently similar microbiological quality (as judged by the presence of faecal indicator organisms). Studies of chemical water quality from rainwater tanks have examined a range of parameters including a variety of metals, nitrate/nitrite, sulfate, combustion products and pesticides, although the amount and quality of data on individual contaminants is variable. Overall, the data suggest that levels of metal contamination are unlikely to exceed Australian Drinking Water Guideline (ADWG) values except where a major source of industrial pollution is located nearby. The results of studies assessing nitrate/nitrite and sulfate levels also suggest that concentrations in water from rainwater tanks in urban Australia are unlikely to exceed ADWG guideline values. Only one study identified in this review assessed the combustion product benzo-( )-pyrene and pesticides. In this very limited data set, the levels of these compounds detected did not exceed the ADWG guideline values. Given the limited extent of data on chemical contaminants in water from rainwater tanks, it is not possible to conclude whether significant health risks from chemical contaminants may be associated with regular rainwater consumption. More information is needed on the quality of collected rainwater in the urban Australian and New Zealand context, particularly with respect to airborne industrial pollutants and vehicle exhausts. The available data do not permit any definitive conclusions to be drawn about the effect of roof or tank materials on health-related water quality parameters. Similarly there is little information relating management practices to water quality, although there is experimental support for the capacity of first flush diversion to improve the quality of collected water. Surveys of householders indicate that cleaning of sludge from tanks is generally rare, although cleaning of gutters is more frequent.

3 The published literature contains a small number of reports of disease outbreaks and individual cases of illness attributable to rainwater. The bacterial pathogens Salmonella and Campylobacter have caused outbreaks of gastroenteritis related to rainwater consumption. These pathogens are commonly carried by birds and are likely to represent the greatest microbial risk from rainwater consumption. Case-control studies of specific pathogens have supported the role of rainwater as a source of Campylobacter infection but not Cryptosporidium infection. Given that individual rainwater tanks normally supply only a small number of people, the low number of outbreak reports does not necessarily rule out significant risks of illness from rainwater tanks. Passive surveillance systems are unlikely to detect small outbreaks as only a minority of people with gastrointestinal illness seek medical attention, and only a small proportion of those who do so have a faecal specimen examined for pathogens. To investigate the relationship between tank rainwater consumption and gastroenteritis in South Australia, a prevalence survey of 9,500 four year-old children was undertaken and this was followed up with a longitudinal cohort study of gastroenteritis among 1000 four to six-year-old children, selected on the basis of their tank rainwater consumption (Heyworth, 2001). This study found that in South Australia, children drinking tank rainwater were not at a greater risk of gastroenteritis than children drinking public mains water. Only two epidemiological studies have compared overall rates of gastrointestinal illness between people drinking rainwater and people drinking from reticulated water supplies. Both studies were conducted in South Australia and examined children in the 4 to 6 year age group. The two studies gave somewhat differing results, but overall suggest that consumption of water from rainwater tanks does not pose a significant health risk in relation to microbial pathogens for children (and by inference adults) in the general community. Human exposure to microbial and chemical contaminants of water supplies occurs directly via ingestion, inhalation and skin contact. The relative importance of these exposure routes differs for different types of contaminants. The ADWG define health-related guideline values on the basis of ingestion exposure although for some chemical contaminants dermal absorption and/or inhalation may also be significant routes of exposure. Overall, the nature of the potential health risks and the importance of the different exposure routes are not intrinsically different for rainwater and conventional tap water supplies. However given the available evidence that water from rainwater tanks is more variable in both microbial and chemical quality than conventional tap water supplies, it would be expected that higher risk situations would occur more frequently with rainwater supplies. Infections by microbial pathogens potentially found in collected rainwater generally pose acute (short term) risks to health. These risks may range from mild disease of one or a few days duration through to severe illness for several weeks, and in rare cases death may result. In a small minority of infected people, longer term health effects may occur although the infection persists only a short time. Rainwater System Design and Use Guidelines Many Local Councils, State Health Departments and Industry Associations have either have developed, or are in the process of developing, guidelines for use of rainwater harvesting systems. These guidelines have been developed to help optimize water quality.

4 Key aspects of many of these guidelines are: 1. Incorporating gutter mesh systems - to help ensure gutters do not become blocked with leaves and debris; to prevent mosquito breeding habitats. 2. Regular inspection, and if necessary, cleaning of gutters and inlet mesh filters 3. Fitting rain heads at gutter downpipes - to separate leaves and debris from the flow of water; to keep mosquitoes out of pipe systems to the tank (especially in "wet" systems) 4. Preventing the first flush rainwater from entering the tank - to reduce the amount of roof pollutants 5. Insect proofing all tank openings (inlets and overflow outlets) - to prevent mosquitoes breeding 6. A clean, impervious roof made from non-toxic material 7. The absence of lead flashing and lead based paints (on older houses and buildings) 8. Tank taps or draw off pipes that are at least 100 mm above the tank floor (alternatively, a floating arm draw off valve) 9. A tank floor which slopes towards the sump and washout pipe 10. A well covered manhole for easy access and inspection 11. Desludging may be required every 2-3 years. 12. Keeping roof catchments clean and clear of moss, lichen, debris and leaves. 13. Cutting back trees and branches that overhang roofs. 14. Inspecting tanks annually and cleaning them out if necessary 15. Testing the water periodically 16. Disinfection of the supply from the tank if contamination is evident Rainwater Disinfection It is apparent from the guidelines described above, local councils and health authorities concentrate on physical cleanliness to ensure rainwater of good potable quality. Rainwater tanks may pose indirect health risks by providing breeding sites for mosquitoes which are vectors for disease transmission. In the past, rainwater tanks have been demonstrated to provide breeding sites for the Dengue virus vector, Ochlerotatus aegypti, in outbreaks in Queensland and the Torres Strait. (please note that the fever was spread by mosquito rather than consumption of the rain water). At present there appears to be no evidence implicating rainwater tanks in transmission of other vector-borne diseases in Australia. Whilst no one can argue that keeping rainwater systems physically clean and also clear of Mosquito breeding is important, the guidelines only call for disinfection of the supply if contamination is evident. This is surprising to the author given that the risk of disease or illness from drinking rainwater is considered (by the limited studies to date) to be at least equal to that of consuming municipally treated water. A great deal of care is taken on municipal water supplies to ensure that they are continuously physically clean and disinfected. This is traditionally carried out by chemically cleaning and filtering the water followed by the addition of chlorine to oxidize pathogens. In recent years membrane filtration and ultraviolet light disinfection has also been employed on municipal systems.

5 With close to 3 million Australians and New Zealanders drinking predominately non disinfected rainwater on a daily basis this would seem to be worthy of more public health discussion and action. Recommending disinfection only after proven contamination of the rainwater is hardly a proactive guideline. So why not take the same public health approach to rainwater as for municipal water? The answer appears to be that domestic rainwater consumption has been in the private domain and as such has had no direct public funding and interest from water and public health authorities. The very few health studies conducted to date is testimony to this. The exact incidence of disease and illness due to rainwater consumption in Australia and New Zealand has simply not been quantified. Furthermore, as discussed above, the risks of illness and disease are naturally limited to the householders subject to a contaminated rainwater. There is therefore a natural limit to the risk to the public. On the contrary the contamination of a municipal water supply can cause illness and even death to thousands or even millions of people with one incidence or outbreak. Recognising the opportunity Davey Water Products, Davey, has taken a market based approach to the problem of rainwater disinfection. Davey has been supplying rainwater pumps and pressuring systems into the Australian and New Zealand markets since In 2005 Davey acquired a private water treatment company in New Zealand (Contamination Control Limited) that had built up a business providing filtration and disinfection systems for rural and metropolitan households. In combination with Davey s expertise in rainwater pumping and household pressurization the subsequent filtration and disinfection of the rainwater was a natural fit. Davey has now embarked on a product development path that is providing one stop pumping and disinfection solutions for the rural householder. The technology package was introduced into the Australian market in early 2006 and since that time the uptake has been significant. Davey has discovered that there is indeed a latent market for rainwater filtration and disinfection if delivered in a user friendly, effective and economic manner. Technology solutions being offered by Davey Davey is taking a simple three step process to the market for rainwater disinfection. Step 1 is a course 20 micron pleated filter to trap large suspended solids and protect the finer filter. Step 2 is a 1 micron depth filter capable of physically removing cysts such as Cryptosporidium and Giardia. Step 3 is an Ultraviolet light disinfection system for the disinfection of remaining cysts, bacteria and viruses. Ultraviolet light disinfection systems utilise the ability of certain generated wavelengths of light to disrupt the DNA of cysts, bacteria and virus rendering them incapable of infection. The system is sized for small, medium and large households with flow rates of 40, 75 and 130 litres per minute respectively. The system has been matched to common household water pressure systems for ease of selection by the consumer.

6 Ultraviolet light disinfection is ideal for the treatment of rainwater due to the high UV transmission rate of rainwater. UV transmission is a measure of how much of the UV light is transmitted through the water with distilled water having a transmission of 100% by definition and rainwater typically 90%. Various impurities in water can reflect or adsorb the UV light and lower its effectiveness at inactivating microorganisms. By contrast typical municipal water supplies range from 85 to 95 % transmission. An alternative being offered by Davey is a chemical disinfectant based on dilute, stabilized hydrogen peroxide and trace parts per million of silver (Davey Acquasafe). Measured quantities of the solution are added to the rainwater tank in a single dose with a residual detected by test strips at the kitchen tap. The householder can use the test strips to determine when a new dose is required after several weeks. The chemical disinfects by oxidizing the cysts, bacteria and virus and utilizing the known biocidel properties of trace silver. Both systems are economic, effective and easy to maintain for the householder. In combination with correctly maintained rainwater collection systems these water treatment solutions can now provide rural households with equal or superior water quality to that provided by municipal water authorities. Spread of Rainwater Tanks into Metropolitan areas and future trends In Australia the extended drought and infrastructure based water shortages has caused state based water saving legislation to be introduced for new residential homes. Each state legislation is different but the net effect has been a dramatic rise in installation of rain water tanks in metropolitan households. The captured rainwater has been predominately used for garden watering and connection to toilet flushing and washing machines. The author estimates that as many as 100,000 water tanks per annum are currently being installed in metropolitan Australia. Typically tank sizes are 1000 to 5000 litres with 2000 litres appearing to be the most popular size. These tanks are much smaller than their rural counterparts as they are not being used for all water use and space is at a much higher premium. By connecting to toilets and washing machines up to 40% of a typical household s usage can be saved. A typical metropolitan rainwater tank installation will employ modern interconnection devices that switch seamlessly between rainwater and mains water (the Davey Rainbank system is one such interconnection device). In this way the consumer is never out of water an all too common issue for rural households not connected to municipal mains water. As discussed above around 3.2% of capital city people currently drink rainwater. Adelaide is the exception with 12.6% of people drinking rainwater. In Adelaide (and as is likely for the other capital city rainwater users) the rainwater is captured only for specific potable use and separately plumbed municipal water is used for showering and other household uses. Often the rainwater is supplied to a kitchen tap under gravity and without filtration and disinfection. As we have seen the nature of microbiological risks is likely to be similar in urban and rural settings, however for chemical contaminants there may be significant differences between urban and rural areas. In urban areas a greater influence of traffic emissions and industrial pollution would be expected relative to rural areas, while in rural areas there may be more potential for contamination by agricultural chemicals such as pesticides and fertilisers.

7 In both rural and metropolitan areas due diligence and care needs to be taken by the consumer that this type of pollution or contamination is not an issue near their home. If this is suspected it would be recommended that rainwater samples be thoroughly tested for potable use. There are many water laboratories available that can provide such services at relatively low cost. One possible example of this would be homes close to large airports that may have the risk of organic fuel residuals falling on the roof. Even these issues are possible to mitigate with appropriate water treatment. For example, trace levels of a variety of organic compounds can be removed from water effectively by activated carbon filter cartridges. This applies equally if a rural dweller suspects pesticide residuals for example. As discussed above there has been very limited work carried out in Australia and New Zealand on the risks of such rainwater contamination in either rural or metropolitan areas. The recent influx of water tanks into Australian cities is triggering the question of using the newly available water more broadly than just for gardens, toilets and washing machines. These uses are considered of very low risk for exposure to pathogens by ingestion. But why not for showering or even for whole of house use? Work has been done in Newcastle (Coombes, Figtree Place) for the use of rainwater to supply household hot water services as a low risk option since the high water temperature can inactivate enteric pathogens. The research at Figtree Place showed that microbiological water quality is substantially improved by passage of rainwater through hot water services, although further work is required to confirm the required minimum temperature. Existing Australian guidelines recommend that a water temperature of at least 60ºC is maintained in hot water service tanks in order to avoid growth of Legionella bacteria. This temperature also appears to be adequate to inactivate enteric pathogens. The Figtree Place studies indicate that a 40% to 50% reduction in mains water use may be achieved by substituting rainwater for garden watering, toilet flushing and hot water services. To move to whole of house rainwater use in the metropolitan area a simple step of adding filtration and UV disinfection could be taken by the consumer. As a double barrier protection against pathogens it would also be possible to add a chemical disinfectant such as the Davey Acquasfe or other such oxidizing chemicals to ensure a residual at the kitchen and other household taps. Alternative double barriers could also include point of use filters at the kitchen tap. There is a range of such filters readily available from Davey and other suppliers. With approximately 3 million Australian and New Zealanders already drinking rainwater as their primary potable water comprehensive studies on rural and metropolitan rainwater quality are well overdue. With an additional estimated 100,000 rainwater tanks being installed in the Australian metropolitan area each year the number of people deciding to go whole of house and drink the rainwater will no doubt grow. In Australia Davey and other water industry suppliers are experiencing an unprecedented increase in demand for rainwater interconnection systems, rainwater pumps, pressurizing systems and rainwater treatment systems.