Introduction

Problems with iron are most likely to arise at the treatment plant or within the distribution network rather than the home plumbing system. However, corrosion can result in a number of metals or alloys from which pipework or plumbing fittings are made contaminating drinking water. The most important of these are lead, copper, zinc and iron.

Corrosion

Most types of corrosion involve electrochemistry. For corrosion to occur the components of an electrochemical cell are required, i.e. an anode, a cathode, a connection between the anode and cathode (external circuit) and finally a conducting solution (internal circuit), in this instance drinking water. The anode and cathode are sites on the metal pipework that have a difference in potential between them, which may be the same metal or different metals. When this occurs then oxidation (the removal of electrons) occurs at the cathode, which is negatively charged. In practice metal dissolution occurs at the anode, releasing the metal into solution (Figure 27.1).

Corrosion cells form on the same piece of metal where there are adjacent anodes and cathodes. These are due to the non-uniformity of the surface and can be caused by minute differences in the pipe surface formed during manufacture, or by stress imposed during installation. Any imperfections in the pipe will create tiny areas of metal with different potentials.

Corrosion is more rapid where two different metals are coupled together. This is known as galvanic corrosion. The most serious situation is where a copper pipe is used to replace a section of lead pipe (Section 27.3). The conducting solution (electrolyte) is the water, the copper pipe is the cathode and the lead pipe is the anode. The lead pipe slowly corrodes, releasing the metal into solution. Metals can be listed in order of their tendency to corrode or go into solution, i.e. the galvanic series. The metals and alloys most commonly used in water treatment and distribution can be placed in electrochemical order, which is the decreasing order in which they tend to corrode when connected under ordinary environmental conditions.

Sources in water

The nitrogen cycle has altered drastically in the past 50 years with nitrate steadily accumulating in both surface and ground waters. Anthropogenic sources of nitrogen, of which nitrogen-based fertilizer is by far the greatest, now exceed the amount of nitrogen fixed by natural processes by 30% (Fields, 2004). Organic and inorganic sources of nitrogen are transformed to nitrate by a number of processes including mineralization, hydrolysis and bacterial nitrification. The resulting nitrate not utilized by plants or denitrified to nitrogen gas under anoxic (reducing) conditions leaches into surface and ground waters. However, recent evidence has shown that the rapid increase in nitrates in water sources is due not only to increasing fertilizer usage and the spreading of livestock wastes but also to the release of nitrogen oxides (NO x) from burning fossil fuels. This increase infixing nitrogen from the air to produce ammonia fertilizers while at the same time releasing nitrogen from the use of fossil fuels has led to the creation of a man-induced nitrogen cycle that dominates the original natural cycle. The nitrogen cascade, as it is widely known, is resulting in acid rain formation, global warming, ground level ozone and smog formation, and increasing runoff and leaching of nitrogen into water resources (Figure 5.1) (Hooper, 2006).

Nitrate fertilizer is the single most important and widely used chemical in farming. Its use on farms throughout Europe has rapidly increased over the past 30 years in particular, reaching the current phenomenal levels. In the UK the use of nitrate fertilizer increased from just 6000 tonnes per year in the late 1930s to 190 000 tonnes by the mid 1940s. This rise was due to the need to grow more food during the Second World War. However, the reasons for the increase in its annual use to a staggering 2 000 000 tonnes by 1995 are less clear.

Introduction

In its purest state water is both odourless and tasteless; however, as inorganic and organic substances dissolve in the water, it begins to take on a characteristic taste and sometimes odour. Generally, the inorganic salts at the concentrations found naturally in drinking water do not adversely affect the taste; in fact, many of the bottled mineral waters are purchased because of their characteristic salty or sulphurous taste. Both tastes and odours are caused by the interaction of the many substances present. These may include soil particles, decaying vegetation, organisms (plankton, bacteria, fungi), various inorganic salts (for example, chlorides and sulphides of sodium, calcium, iron and manganese), organic compounds and gases (Cohen et al., 1960; Baker, 1963). Water should be palatable rather than free from taste and odour, but with people having very different abilities to detect tastes and odours at low concentrations this is often difficult to achieve. Offensive odours and tastes account for most consumer complaints about water quality.

In 1970 it was estimated that 90% of water supplied in the UK occasionally suffered from odour and taste problems (Bays et al., 1970). This is similar to the figure for the USA and Canada where 70% of water supplies are affected. The situation has improved enormously over the past 36 years due largely to the introduction of the EC Drinking Water Directive. According to the annual reports of the Drinking Water Inspectorate (www.dwi.gov.uk) the problem is now much smaller. However, odour and taste problems can be very transitory phenomena, so it is unlikely that the standardized monitoring carried out by some water supply companies involving taking just four or five samples a year will detect all but the most permanent odour and taste problems.

Standards and assessment

There are two widely used measures of taste and odour. Both are based on how much a sample must be diluted with odour- and taste-free water to give the least perceptible concentration.

Since writing the first edition there have been enormous changes in the water industry especially in the way drinking water quality is perceived and regulated. That first edition was written at the same time as the 1993 revision of the World Health Organization (WHO) guidelines as published, which has subsequently resulted in the revision of all the major drinking water standards, including those covering the European Union and the USA. That early edition reflected those changes. So the preparation of this new edition was timed to coincide with the publication, late in 2004, of the latest revision of the drinking water guidelines by the WHO, which has adopted a more rigorous health-based approach in setting guidelines. These new guidelines have been used as the basis of this new edition.

The problems associated with global warming leading to regional changes in climate and water availability are seriously affecting sustainability of supplies as well as seriously impacting on quality. Advances in chemical and microbial analysis have revealed that water contains many new contaminants that were previously undetectable or unknown, constantly presenting water utilities and regulators with new challenges. Also the recent terrorist attacks have demonstrated how vulnerable water supplies are to contamination or disruption. Thus, while the existing risks remain and need to be dealt with on a day-to-day basis, these new problems require innovative technical and management solutions. The aim of this new edition is to give an overview of the current and emerging problems and what can be done to solve them.

This new edition has been extensively updated and expanded using a different framework. It now comprises of 31 chapters clustered into 5 distinct parts, each dealing with a separate element of the water supply chain. Part I. Introduction to water supply comprises of three introductory chapters. The first deals with the fundamentals of the water industry: how much water is used; what is required by consumers in terms of quality; and the operation, management and regulation of the water utilities.

Introduction

Chemical analysis can only be used for the assessment of water treatment efficiency and to monitor compliance to legal standards, while biological examination of water is used to detect the presence of algae and animals that may affect treatment or water quality, and to identify possible defects in the distribution network. Microbial safety of water is the historical and fundamental reason for water treatment, with pathogens monitored using complex, and often costly, techniques. The objective of water treatment is to remove pathogens rather than to act as a reservoir or source of micro-organisms, although the very act of treatment can inadvertently result in periods of high contamination as seen with Cryptosporidium (Section 13.2).

Monitoring pathogens

Pathogens are outnumbered by the normal commensal bacterial flora in both human and animal intestines, so they can only be recovered by filtering relatively large volumes of water (≤2 1). Isolation of pathogens requires specific and complicated tests using special equipment; with positive identification often only possible after further biochemical, serological or other analysis. This makes routine monitoring of individual pathogenic micro-organisms in drinking water both difficult and expensive. It is currently impracticable to examine all water supplies on a routine basis for the presence or absence of all pathogens, although the developments in gene probe technology may well make this possible in the future. To overcome this problem a rapid and preferably a single test is required, the theory being that it is more effective to examine a water supply frequently using a simple general test, as most cases of contamination of water supplies occur infrequently, than only occasionally by a series of more complicated tests. This has led to the development of the use of indicator organisms to determine the likelihood of contamination by faeces.

Microbial slimes in distribution pipes

Microscopic organisms such as bacteria and fungi are common in water mains. They grow freely in the water, and more importantly form films or slime growths (bio films) on the side of the pipe wall, which makes them far more resistant to attack from residual chlorination (Chapter 25). In an operational sense water supply companies find bio film formation undesirable as it increases the frictional resistance in the pipes, thereby increasing the cost of pumping water through the system. Certain bacteria attack iron pipes increasing the rate of corrosion, and can also affect other pipe materials. In terms of water quality, microbial bio films can alter the chemical nature through microbial metabolism, reducing dissolved oxygen levels and producing end-products such as nitrates and sulphides. Odour and taste problems have been associated with high microbial activity in distribution systems, as have increased concentrations of particulate matter in drinking water (Chapter 21). The microbial bio films are also the major food source for larger organisms that are normally found in the bottom or at the margins of reservoirs, lakes and rivers.

Many upland rivers contain water of an exceptionally high quality, with a low density of suspended solids and good microbial quality. Such supplies may only receive rudimentary treatment, so very small animal species and juvenile forms of larger species can enter the mains in large numbers. Some animals are able to penetrate filters, or can enter the distribution system due to operational problems at the treatment plant. This means that populations of small animals are common in distribution systems. Free-swimming (planktonic) species such as Daphnia (water fl ea) are unable to colonize the mains, whereas many of the naturally occurring bottom sediment dwelling species (benthic) such as Cyclops, Aelosoma and Nais easily adapt to life in the mains and even form breeding populations. The species which give rise to most complaints are not necessarily those species which enter the mains in the greatest numbers from the resource; rather it is those which are able to colonize and reproduce successfully within the distribution system.

Introduction

The realization of high drinking water quality requires integrated control measures at all points along the supply chain starting with catchment management and the protection of water resources, throughout treatment, storage and distribution, as well as the home plumbing system. Thus, maintaining high-quality drinking water is extremely expensive, and may at times be unnecessary where no threat to human health has been identified. Therefore, drinking water standards must be a compromise between cost and risk to both consumers and the environment. However, water scarcity and sustaining the increasingly high levels of demand may compromise standards, which must be realistic and achievable under local operating conditions.

The World Health Organization (WHO) has proposed a preventative management framework to ensure safe drinking water (Figure 2.1). This comprises five components: (1) health-based targets; (2) assessment of the supply system to ensure that targets can be met on a continuous basis; (3) operational monitoring; (4) assessment and monitoring procedures within a management plan that also incorporates operational and emergency procedures; and finally (5) independent surveillance of the entire system, which feeds back to all the other components of the framework. Also included within this management framework is the constant revision of the published health-based literature in relation to drinking water quality and the effects of individual substances and pathogens found in water. This water safety management framework is universally being adopted both by rich and poor countries alike (Section 2.4).

Development of quality standards

Ideally water quality standards are based on health-based targets, which in turn are based on a review of the current epidemiological and medical research. For that reason, drinking water quality criteria, from which standards are derived, are constantly being reviewed with standards equally likely to be tightened or relaxed depending on the most reliable information. Health-based targets offer a wide range of benefits during their formulation, implementation and subsequent evaluation (WHO, 2004).

Entry to the home

Houses are connected to the mains by the service pipe (Figure 20.3). The connection from the mains to the boundary stopcock is known as the communication pipe, and this is owned and maintained by the water supply company. The boundary stopcock, as the name suggests, is located just outside the boundary of the property served, with the stopcock being a control valve that turns off the water supply to the house. It is usually buried 1 m below ground, at the bottom of an access chamber known as the guard pipe; which can be a short piece of any suitable pipe, the top access being protected by a small metal cover. The stopcock can be turned on or off using a long-handled key, the exact nature of which depends on the type of handle on the stopcock itself. It is switched off by turning the key in a clockwise direction. From here the service pipe, which is now known as the supply pipe, carries the water to the house. It rises slightly to ensure that all air bubbles escape. From the boundary stopcock onwards all the pipework and the appliances are the householder's responsibility. The supply pipe must be at least 750 mm below the ground at all times to protect it from frost. It usually enters the house at the kitchen and rises up from the floor underneath the kitchen sink. The pipe (the rising main) continues directly upwards either to the cold-water tank (often referred to as the cold-water cistern because it is operated by a ballcock valve), or to feed the other cold-water draw-off points around the house. There should be an indoor stopcock positioned where the pipe enters the house and before the connection from the rising main to the sink to be able to cut off the supply to the house. The kitchen tap should always be connected directly to the rising main. If the supply pipe enters the house at another point, for example through a cloakroom or garage, then the stopcock will be fitted there.

Introduction

The vast majority of us have our water delivered to our homes fully treated and ready to consume. We turn on our taps and expect all the water to be safe and palatable to drink at any time during the day or night. Similarly we expect water, at the correct pressure, to operate our washing- and dishwashing-machines, our showers and other household appliances. In fact it is only until there is a water shortage or a problem with quality that any of us actually even think about water. That is not the case for those on private supplies who have to maintain their own borehole and pump. For this group water quality is often a continuous cause of concern. So what are the options for those on public and private supplies who are concerned about their water quality? Bottled waters offer a short-term alternative to mains supply for consumptive purposes (Section 29.2), while home, or point-of-use, treatment systems offer a long-term solution to problematic water (Section 29.3). Harvesting the water from roofs and recycling water from washing-machines, showers and baths has become increasingly popular for supplying water for external uses such as car-washing and watering the garden, although this water is normally unsuitable for drinking without treatment (Section 29.4).

Bottled water

The increase in the consumption of bottled water worldwide is phenomenal with estimated global sales around 1.55 ' 1011 litres in 2004. Compound annual growth rates (1999–2004) vary between 4.2% in France, which already has a high per capita consumption rate, to 20.9% in China, where per capita consumption is still comparatively low. The average growth rate worldwide is 9.4% (Table 29.1a). In 1980 just 30 million litres of bottled water were drunk in the UK, rapidly rising over the intervening period to between 200 and 250 by 1991 and to 1770 million litres by 2002.

Introduction

Water that is bacteriologically pure when it enters the distribution system may undergo deterioration before it reaches the consumers' taps. Contamination by micro-organisms can occur through air valves, hydrants, booster pumps, service reservoirs, cross-connections, back-syphonage or through unsatisfactory repairs to plumbing installations. Invertebrates found in distribution networks can also harbour and concentrate a range of micro-organisms (Section 24.5) (Table 24.1). Further problems can also arise within the domestic plumbing system (Chapter 28).

The main danger associated with drinking water is the possibility of it becoming contaminated during distribution by human or animal faeces. This was the case in the Bristol outbreak of giardiasis in 1985, when contamination occurred through a fractured main. A major outbreak of typhoid fever occurred in 1963 in Switzerland when sewage seeped into the water mains through an undetected leak in the pipe. There are many more examples indicating that the microbial quality of water is potentially at risk while in the distribution system. Uncovered service reservoirs can also be a major source of contamination, especially from birds, and there is growing concern about the safety of drinking water while in the distribution system from terrorism (Section 25.4).

Microbial contamination

Usually the mains is under considerable positive pressure; however, back-syphonage can occur in the distribution system if the water pressure drops and there are faulty connections or fractures in the pipe. In this way contaminants can be sucked into the distribution system. The problems are more likely to occur when water supply pipes are laid alongside sewerage systems. They should be as remote as possible from each other, although in practice this is very difficult.

On passing through the distribution system, the microbiological properties of the water will change. This is due to the growth of micro-organisms on the walls of the pipes, which form a thin bacterial layer, and in the bottom sediments and debris. Although not usually the source of serious health problems, non-pathogenic bacteria can result in serious quality problems, causing discolouration and a deterioration in taste and odour (Chapter 21).

Introduction

Under normal circumstances each one of us requires between 1.8 and 2.0 litres of water each day in order to maintain a healthy body. In practice people drink very little water on its own; rather they drink a wide variety of beverages made from water. Tea, for example, contains very high levels of aluminium, fluoride and polycyclic aromatic hydrocarbons (PAHs) as well as elevated levels of many other metals and compounds (Flaten and Ødegård, 1988; Lin et al., 2005; Cao et al., 2006). Canned carbonated drinks can have very high levels of aluminium as well as other compounds and metals (Table 15.2). So our exposure to contaminants is more often related to what we drink and eat rather than drinking water per se.

However, in recent years there has been an enormous upsurge of interest in drinking water, which has been reflected in record sales of bottled water (Table 29.1) and the use of water coolers. While bottled water has become fashionable, the public's perception of tap water remains negative (Section 31.3). Yet in reality tap water in the majority of developed countries is of a higher quality than ever before, and equal in quality to bottled waters. So should consumers be concerned over drinking water quality?

Like other food manufacturers, the water utilities have a unique relationship with their consumers who trust them to provide food and water that is completely safe to consume. However, problems can and do arise.

Problems can be categorized into three areas. (1) Traditional problems that water treatment normally effectively deals with, such as infectious diseases associated with waterborne pathogens. (2) Accidental problems that result from poor operational practice or accidents such as elevated levels of aluminium in water, the breakthrough of protozoan oocycts (e.g. Cryptosporidium) or spillages of contaminants into water resources that are not detected early enough.