Closing the SDG access gap – the challenge of intermittent supply

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With 10 years remaining on the Sustainable Development Goal clock, time is short to tackle intermittent water supply, which undermines efforts to achieve the goal of universal and equitable access to safe drinking water. The International Water Association is ideally placed to catalyse change, having hundreds of members in impacted countries and a dedicated Specialist Group on the topic, writes Kala Vairavamoorthy.


We have long known that water’s crucial role in sustaining human settlements and bolstering their resilience cannot be overstated. The ongoing COVID-19 pandemic, with its attention on handwashing, has reminded us of this fundamental importance. This same call for handwashing has also exacerbated the strains on water supplies in cities of developing countries, where the supply systems are operated intermittently. It has highlighted the inherent vulnerability of the people these systems are intended to serve.

Nearly one billion people receive water from piped networks that experience intermittency. Furthermore, nearly 41% of piped water systems in lower- and middle-income countries operate intermittently. The twin parameters of low pressure and the time for which taps do or do not flow define the experience of intermittent supply from the consumer’s perspective.

This experience varies widely. For example, in a study conducted by the Asian Development Bank looking at 18 utilities in India, the duration of water supply varied from 20 minutes to 12 hours per day, while the average pressures at consumer connections ranged from 0-10 metres (0-14 psi). Unreliability of water supply is also a frequent issue among those already impacted by limited availability. The time of when water is available can vary on an almost daily basis, leaving many paralysed by an inability to forward plan or to allocate their (limited) resources effectively. The only reliable thing about their supply is its unreliability!

How did we reach this point, where the gap between the prospect of water being available at the turn of the tap, any time of day or night, and the reality for consumers is so great? This is a question I have pondered and interrogated for many years. Indeed, I began researching intermittent water supply (IWS) in 1990 as a PhD student – the title of my thesis was ‘Design and control of intermittent supply’. I subsequently undertook several large research projects funded by the UK’s Department for International Development to develop international guidelines.

Many factors come into play, but IWS is almost always adopted by utilities as a reactive strategy. This can be a rationing response to a supply-demand deficit, exacerbated by unplanned and rapid urbanisation, as well as other constraints, such as irregular electricity supplies and poor management of deteriorating infrastructure.

The impacts of intermittent supply

This is not to say that ambitions should focus only on achieving a continuous, 24/7 supply – indeed, I address this below. But it is certainly the case that intermittent operation of water supply systems leads to some highly negative outcomes.

Current data show that 97% of utilities in South Asia operate intermittently. In India alone, it is estimated that at least 200 million people are connected to IWS systems. Keeping in mind this scale of the issue, these negative consequences of intermittent supply are incompatible with Sustainable Development Goal (SDG) 6 – to ensure universal and equitable access to safe and affordable drinking water.

Inequitable supply: Consumers served by intermittent systems are generally not satisfied with the amount of water they receive. Consequently, they try to maximise the amount they draw from the system during supply hours. Often taps are kept open for the duration of the supply period, and the amount consumers are able to collect depends on their localised pressure conditions. This puts those who are located far away from the headworks or at higher altitudes in the service area at a disadvantage. The unfairness this presents is compounded by the fact that cities with IWS have chronically low pressure. Consumers collect and store water when the supply is on to meet their demand through the off-hours. If the supply cycle is short, this means that all consumers may draw their entire water demand within this very short period. This results in larger than expected flows in the pipes (much larger than the designed peak flows), causing high pressure losses, which result in low pressures at consumer connections.

The inequity of IWS can be viewed in a broader sense, too. There is a contrast with the experience of people served by a continuous supply. There the flow in the supply network is a direct response to the demand of the consumer, meeting needs as and when they arise. In the case of IWS, the supply system dictates consumer behaviour – where the consumer needs to be present at the tap at a time when the system chooses to supply them, and where their diurnal water consumption is decoupled from the supply system.

Contaminated water: Alongside the obvious implications for water quantity, IWS brings with it concerns around water quality. This undermines the core ambition of water supply systems – that of delivering water that is safe.

Concerns around quality arise on a number of fronts.

In particular, interruption of water supply leads to periods of zero pressure during non-supply hours, allowing contaminants to enter through broken or cracked pipes. These contaminants, which are in close proximity to the water network – are the result of poor or inadequate sanitation and drainage, raising the prospect of faecal contamination.

When flow restarts, pipes transition from empty to pressurised and this causes a flushing effect of the microbial contaminants that have entered (and grown) in the network during the stagnant periods. Indeed, a decrease in water quality at the beginning of supply cycles has been observed in several IWS systems, with higher concentrations of faecal indicator bacteria and turbidity detected during flushing when compared to the rest of the supply cycle. Furthermore, by its very nature, IWS requires household storage, and these storage tanks are often at risk of contamination.

The health risks associated with such aspects of IWS are becoming increasingly clear.

Studies have shown continuous supply to be associated with a lower incidence of faecal-oral diseases in low-income households. In epidemiological investigations of outbreaks, IWS has been linked to diarrhoeal diseases, including amoebiasis, typhoid, and cholera, as well as infectious hepatitis. Each year, IWS may account for 17.2 million infections causing 4.52 million cases of diarrhoea, 109,000 diarrhoeal DALYs (diarrhoeal disability-adjusted life years), and 1560 deaths. The burden of diarrhoeal disease associated with IWS likely exceeds the WHO health-based normative guideline for drinking water of 10-6 DALYs per person per year.

The prevalence of IWS, combined with its association with poor drinking water quality, make this an important focus for action. This is particularly significant given that piped water supplies rely on multiple barriers to ensure safety of the drinking water, such as pipeline integrity, positive pressure, and residual chlorine levels. These are more likely to fail simultaneously in the resource constrained settings where IWS is prevalent.

Further fundamental and applied research is required on various elements of this topic, including the impact of the first flush effect in intermittent systems on microbial water quality. We need to explore further the premise that the protective impact of continuous pressure could be greater in low-income neighbourhoods, where unsanitary conditions may facilitate pathogen intrusion into pipes under intermittent pressure. Any improvements in municipal water quality would therefore potentially have a bigger health impact for low-income residents who currently consume this water untreated.

More broadly, water operators still need to fully understand how operation of IWS systems can affect water quality. Armed with this better understanding, they can develop strategies for improving water quality within the distribution system right through to the taps of the consumer.

Coping costs and inconvenience: For consumers, an intermittent supply is of course likely to be better than no supply at all, but there are many practical challenges.

For a start, intermittent supplies can be inconvenient. The need to rotate supplies means that the timing of supply is often not convenient for users who have to collect water from public taps. They may need to travel long distances, sometimes in the middle of the night, and then queue for hours. It is often women and children who must endure this, bringing about further gender and age-related inequality.

Faced with the realities of an intermittent supply, consumers respond as best they can to satisfy their needs. This means that they incur a range of so-called coping costs to deal with IWS. These costs can relate to the purchase of facilities in which to store water. They can relate to energy costs, perhaps for local pumping because of low pressures, or for boiling drinking water to make it safe. There can also be a need to purchase alternative water supplies, including bottled drinking water. Since the poorest consumers can least afford such facilities, they are likely to be disproportionately affected by IWS.

Wastage of water: We also see that intermittent supply contributes to wastage of what are invariably precious water resources.

This wastage comes in part from the natural response of consumers to their precarious supply. It has been well reported that, because of the irregular nature of IWS, consumers often hoard water whenever possible. This gives them the comfort of the greatest possible security of supply. At the same time, there is a tendency to dispose of any unused stored water when supply resumes, so that the receptacles can be used to collect and store fresh water.

Alongside wastage by consumers, intermittent supply generally goes hand in hand with high levels of Non-Revenue Water and physical losses from the supply network. NRW data from 2018 show that global losses amount to 346 million cubic metres per day. One fifth of these losses are in South Asia, of which 60% is down to physical losses (40 million cubic metres per day). This can be attributed primarily to the deteriorating underground water supply infrastructure.

Meanwhile, the accurate estimation of water losses in piped networks with IWS is a challenge. Methods based around water balancing, such as minimum night flows and district metered areas (DMAs), might not work in systems where outlets are always left open and where local flow control devices are removed to maximise discharge. IWS can also damage water meters through repeated drying and wetting and the creation of vacuums. At the same time, the frequent occurrence of air pockets and consumer storage tanks with float valves cause meters to register incorrect water flows.

As mentioned earlier, low pressure is more prevalent in IWS networks compared to continuously-operated networks, with average pressures reported to be between 0 and 5 metres (0-7 psi) in the IWS network and 10-30 metres (14-43 psi) in the 24/7 network. This becomes a challenge, particularly in terms of billing and efforts to use consumer service connections to monitor the usage of water. As noted above, this diversity of pressure across a network leads to inequitable distribution, with consumers near to the water mains receiving more water than those at the end of the network.

The need for action, but what action?

The numbers around intermittent supply and the impacts set out above – of inequality, contamination, coping costs, and wastage – demand action. Moreover, the very nature of the impacts places this demand for action right at the heart of IWA’s global community. This is the space in which IWA’s Specialist Group on Intermittent Water Supply is ideally placed to lead a transformative agenda on an issue that blights the lives of many.

As we look ahead, ambitions will be very much shaped by expectations of transitioning to 24/7, continuous water supplies. It is important to keep in mind that the conversation around intermittent and continuous supplies revolves around arguments made before the 20th century. The reasoning in favour of continuous supply was that it saves capital costs because a new system built to run continuously “requires smaller mains and pipes” than one intentionally run on an intermittent basis. On the other hand, the case against transitioning from intermittent to continuous was that it would be expensive, as it necessitates the strengthening and rigorous monitoring of the pipes, joints, and fittings to prevent fracture and avoid leakage under dynamic pressure variations.

Though an old conversation, it is one where knowledge is lacking for us to move beyond the realities of where we are today. Certainly, it is clear that the discussion needs to be built around the experiences and the research work of experts in the regions most affected, particularly Africa and Asia. In this regard, we can learn from the diversity of case studies of working with intermittent supply and so evolve appropriate and context-specific solutions that can support a transition from intermittent towards continuous supply.

Fuelling a global transition

Even with an ambition for continuous water supply, the reality for many utilities around the world is that they will need to work with the practical challenges of delivering supplies on an intermittent basis. This is a particular area of opportunity for the IWA Specialist Group to contribute, facilitating exchanges on the many dimensions of IWS. It is a space in which it can look to apply all the latest thinking and technologies that the sector has at its disposal.

With the piped water supply extending rapidly across the globe, we need research that investigates some of the unique characteristics of IWS, such as:

de-pressurisation and pressurisation; secondary network modelling and the associated systems function with respect to pressure deviations and outflows; and links between sanitation provision, pipe condition and microbial contamination and propagation, and so on. Such research will have a fundamental part to play in understanding how best to improve equity, reliability, and water quality in intermittent systems.

Many cities are desperately wanting to escape the burdens of intermittent supply. Our collective energies can help deliver this, such as by combining critical understanding of piped water supply systems with efforts to map underground water infrastructure to ensure the water supply quality for the ‘last mile’.

Awareness raising and capacity building will be especially important, particularly in the case of operators. Armed with greater data, metrics and insight on the issues of IWS, including water quality, they will be better placed to deliver improvements where they are most needed.

Our collective aim is to create a water-wise world. Intermittent water supply represents one of the most glaring gaps in this ambition. IWA’s efforts can play a key role in better understanding the current global situation, identifying challenges on the ground and, in turn, shaping and delivering potential solutions. •

Dr Kala Vairavamoorthy is CEO of the International Water Association