It has been shown that intermittent water supply systems have a large number of associated problems. In addition, it must be noted that IWS systems are very heterogeneous, they range from a simple one delivery pipeline to a system with a complex system of pumps, pipes of varying size and quality, with or without a storage tank, some conforming to national standards  and some built without authorization by private entrepreneurs.

How can any given IWS be converted to a continuous supply system, comparable to water distribution normally seen in the most developed countries of Europe and North America?

A necessary precondition for expanding an existing IWS is that the main water transmission is in good working order and has adequate pressure, and pressure requires electricity. Water demand management is another crucial factor in moving from IWS to continuous water supply, as demonstrated by an important case study in Nagpur (India) in which IWS was converted to continuous water supply in order to learn lessons on how this exercise can be replicated in the rest of the country (Hastak et al., 2017). This study also shows that adequate pressure is a necessary part of supply management, which in turn requires a reliable electricity supply.  

Prerequisite for expanding water supply: Finance first

Let us consider a sample of 16 Least Developed Countries and assess their potential for implementing continuous water supply, based on critical development and capacity factors, which are (1) GDP per capita, (2) potential to obtain foreign exchange through trade or borrowing, (3) the existence and size of electricity production, and (4) the existence of a skeletal network of pressurized water pipes that present the opportunity for extension by connecting additional small diameter pipes to this network. 

Table 2 gathers together some basic data that can be used to assess the potential for continuous supply, either by a simple enrichment of the existing water infrastructure or by means of adding trickle fill systems to the skeletal network of water pipes. For this table, we have chosen countries with high populations that are getting by with erratic and irregular water supply, and in many cases with water sources that are unsafe. That should be clear from the last two columns of Table 2. While this is a one-year snapshot, the problem is chronic low per capita income, chronic lack of foreign exchange, chronic unsafe water, and continued deaths year after year due to unsafe water. 

In order to assess the financial capacity to engage in infrastructure expansion, we collect two types of data: (1) we show, in the third column of Table 2, Exports minus Imports, to assess if the country has NET export earnings, which can be used to finance the purchase of water treatment plants, pipes and pumps; in the fourth column we show if a country has a “Current Account” surplus, which brings in other flows besides exports and imports of goods, such as net remittances of nationals working abroad, who send their money to their “home” country,  to  support  other members of their families. The current account surplus means that the country has “hard currency” balances in foreign banks, which it can spend. If the current account balance is negative, it means that the country is in debt, or that its foreign exchange reserves abroad are falling or turning negative. A current account surplus usually indicates that the foreign earnings can be spent on buying foreign goods, like water treatment plants, pumps and pipes. 

The overall negative balance on the current account year after year means a continual increase in external debt, with growing difficulties in servicing the debt. Hence, Table 2 should be read as the repetition of very similar grim data, year after year, for the last two or three decades for the Least Developed Countries (Easterly, 2001). That means growing external debt. We note that with the exception of Bangladesh and Cambodia (and of course Vietnam), all countries in Table 2 are classified as “highly indebted poor countries.” It is recognized that these countries will not be able to repay their debts; so, the IMF and the World Bank have initiated programs by which a great deal of the external debts may be partially or wholly cancelled, provided the country meets specified conditions.

Table 2 shows that this sample of 16 Least Developed Countries (taken from a UN list of 39) do not yet have the potential  to   earn   enough   foreign   exchange   through international trade to be able to import water treatment equipment and install a network of water infrastructure pipes. In addition, foreign aid will not help these countries as they do not have adequate electricity supply (Table 2, column 5) to carry out a program of water infrastructure expansion.  

The lessons of economic development show that when countries have developed and climbed out of poverty, it has been through domestic income growth, implementing domestic production and import substitution, accompanied by earning foreign exchange through exports. This has been the path followed by Japan, China, Taiwan, and South Korea. Indeed, that is also the path that Vietnam has followed, as shown subsequently. 

A SUCCESSFUL CASE STUDY: INFRASTRUCTURE EXPANSION IN VIETNAM

Vietnam has a population of 97.3 million (IEA, 2019). Over the past 3 decades it has progressed from a low to middle income country; its rate of poverty fell from 94.3% in 1992 to 22.4% by 2018 (Macrotrends, 2022). In December 1986, the government adopted the “Doi Moi” (open door) policy, shifting from a centrally planned economy  to  a  market  oriented one. Vietnam’s transformation from a largely agricultural to an increasingly industrial economy has turned the country, once considered one of Asia’s poorest, into one of its fastest growing. It has emulated China in becoming an export-oriented economy (bottom row in Table 2).

The Asia Development Bank (ADB) has been a major partner in assisting Vietnam in urban water supply and sanitation. It has provided around $430 million (slightly less than 50% of the total external assistance in the sector) to Vietnam since 1993 (Asia Development Bank, 2009). The ADB has evaluated the implementation and performance of three loans and all were deemed to be satisfactory. Other loans from the World Bank for expanding water infrastructure have also been successfully used and all interest and loan repayments have been fulfilled on schedule. The adoption of market orientation meant the commercialization of all water and sanitation services for all urban areas. Decree 117 in 2007 mandated that all services move to full cost recovery, and provincial water utilities receive no operating subsidy. By 2010 most water supply companies were re­covering their operation and maintenance costs, but budgets were typically set so low that service quality suffered, contributing to widespread problems of poor water quality, low pressure and intermittent supply. To date few, if any, utilities have achieved full cost recovery. A critical obstacle here has been the reluctance of People’s Party Committees to raise tariffs to commercially viable levels. Nevertheless, great strides have been made, especially first in urban areas.

Vietnam began to set national targets for rural water supply and sanitation in 1999. In 2000, a 20-year plan, the first National Strategy for Rural Water Supply and Sanitation was adopted, and a second Plan was issued for 2006-2010. The total annual investment requirement, according to the Water Supply Program of the World Bank 2014 report, was as follows: rural water supply: $520 million, of which only a third had been secured by 2014; urban water supply: $1.04 billion, of which one-eighth had been secured by 2014. Nevertheless, as can be seen from the evidence given subsequently, Vietnam is credit worthy; and the borrowing agent is the Bank of Vietnam, which has always met its interest paying due dates on time, right up to 2022.

The Second Economic Development Plan of 2006 to 2010 proposed a major expansion of water infrastructure; doubling of water supply capabilities for industry and urban areas; provision of drinking water to 80% of urban residents and 60% of rural residents; reduction of flooding in the rainy season and an ensured water supply in cities; and provision for the increasing disposal of solid and liquid waste in the cities.

Electricity and water in Vietnam

A pressurized water  distribution  network,  required  as  a precondition to expansion of the network through trickle fill will need adequate electricity.  This is a brief review of evidence of the adequacy of electric power supply in Vietnam. 

The state-owned Vietnam Electricity (EVN) was formed in June 2006 by converting the vertically integrated former Electricity of Vietnam into a holding company structure. EVN’s operating units, consisting of power plants, regional power distribution companies, and power transmission system operator, have been converted into independent subsidiaries. According to the International Energy Agency (2019), electricity production in Vietnam in 2019 increased by 228.5% from 1990 (Figure 2). As shown at the bottom of Table 2 (last row), per capita electricity production in 2019 was 2,160 kWh. That row also shows a very large trade surplus (exports minus imports) in 2020, and a healthy current account surplus (last row, column 4), which means that Vietnam has adequate foreign exchange for needed imports of water treatment plants and import (or local manufacture) of the necessary water pumps and pipes.

Since its creation in 1996, EVN has had profitable operations. It has financed the rapid expansion of Vietnam’s electricity sector without resorting to significant fiscal subsidies. Key financial performance indicators, such as the debt service coverage ratio, the self-financing ratio, and receivables, have been maintained at prudent limits.

According to the WHO/UNICEF joint monitoring program 2020 report, Vietnam is likely to be on track to achieve universal basic water and sanitation services by 2030 with an increase at the annual rate of 0.8 and 1.9%, respectively. In 2020, 90% of the population had improved water on their premises and 89% had improved sanitation facilities. However, there is a gap between urban and rural areas and among regions. According to a UNICEF report (2021) nearly 2.5 million people in the rural areas do not have access to clean drinking water, and 10 million people, mainly in rural areas, still cannot access basic sanitation facilities (UNICEF, 2021). But that too is being addressed by the adoption of the National Strategy in Rural Water Supply and Sanitation by 2030, with a vision to 2045. The objective of this Strategy is to ensure that over 62 million rural people have access to safely managed water supply and sanitation services.

However, many challenges remain. According to Vietnam’s Ministry of Agriculture and Rural Development, only 51% of rural households have access to water that meets the Ministry of Health’s water quality standard and that 44% of household water supplies that were tested in the study were found to have E. coli contamination. To reduce impacts of unsafe water and sanitation in the rural population, the National Strategy has set new goals for 2045: 100% of rural people will have access to safe and sustainable clean water and sanitation; 50% of rural residential areas will have domestic wastewater collection systems; 30% of domestic wastewater will be treated; 100% of livestock households and farms will have livestock waste treatment (UNICEF, 2021).

But note that surrounding the major cities are rural populations where the National Strategy in Rural Water Supply is being implemented. For example, for the Central Region, a rural supply project loan of US $50 million was obtained from the Asian Development Bank. A total of around 190,000 people in 48,000 households had been provided with piped water by 2017. Also 33 communes also received piped water. The number relying on dug or drilled wells in the communes fell from around 71,000 to 31,000. The ADB evaluation in 2019 showed that this project was a success (Asian Development Bank, 2019). Progress in implementing the strategy continues and the 2030 targets are likely to be met, project by project. Nevertheless, there is scope for optimizing the use of the major water trunk lines through investment in a larger trickle fill network, similar to the one in the City of Hanoi.

THE TRICKLE FILL SYSTEM FOR OPTIMIZING THE USE OF EXISTING WATERMAINS  

A trickle fill system consists of high-density polyethylene (HDPE) piping with the appropriate size and pressure rating being connected to a watermain (Langford et al., 2012). For a water supply line that must meet the requirements of putting out fires, it is recommended that the HDPE pipe has a minimum diameter of 150 mm (6”); for other mainlines without the need for firefighting, a minimum diameter of 50 mm (2”) would be adequate (Figure 3, for a schematic  representation  of  a  trickle  fill system). The system requires that all end-users have on-site potable water storage tanks, called cisterns, as well as their own on-site pressure systems, where necessary. The water is delivered from a reservoir or high-pressure transmission line to a given community by a low-pressure, smaller diameter HDPE pipe main and, eventually, via branches to each individual customer cistern as shown in Figure 3.

To obtain an understanding of how a conventional property is connected to a municipal water treatment plant, considering Figure 4a, which shows water coming to a property directly from a municipal water treatment plant. To compare this with a property with a trickle fill connection (Figure 4b), in which an individual property has its own cistern or water holding tank that mimics a standard cistern in a conventional toilet, except that it is larger. In contrast to the full pressure municipal system, the end-of-the-line pressure of the low-pressure system constantly or “trickle” into each cistern, typically at a rate of approximately 2.3 L/min (0.5 imperial gallons/min) or 1.14 m³/day (300 imperial gallons per day) (Langford et al., 2012). Usually, these systems are designed to maintain a minimum operating pressure of 138 kPa (20 psi) to mitigate the risk of ingress of contaminates from outside sources, especially in the event of a pipeline break (MPE Engineering Ltd, 2005).

Daily flow demands are satisfied over the course of the day from the holding tank rather than flowing instantaneously from a municipal water treatment plant. Since the cisterns’ storage capacities provide for the only needs to be such that it allows the water to flow peak flows, the trickle fill distribution piping can be sized for average flow, translating to smaller pipe diameters, and thus,  lower  costs  (Janzen  et  al.,  2017). Langford et al. (2012) recommend that the minimum piping diameter for the trickle fill branches be 50 mm (2 inch) in order to support future development and zoning changes. Most of the existing trickle fill pipes in Alberta have diameters ranging between 40 mm (1.5 inch) and 150 mm (6 inch) (MPE Engineering Ltd, 2005).

Furthermore, each customer’s cistern is equipped with a flow emitter assembly (Figure 5) which moderates the intake: when the float drops,  the  float  valve  opens  and allows the water to flow in at a rate dictated by the flow restricting orifice; when the float rises to the top, the valve closes and stops the inflow of water (Regional Municipality of Wood Buffalo, 2018). Typically, the water is distributed throughout each home by an automatic booster pump, often located in the bottom of the cistern. Each cistern should be sized such that it can provide the household peak demand which depends on factors such as  the  number,  age,   gender,   and   behaviors   of   the residents as well as the home’s plumbing fixture characteristics.

Some valves and booster pumps for pressure control may also be required on a low-pressure system, depending on factors such as geography and expected loading; however, less of these will be required than on a conventional full-pressure system. Furthermore, installing flow restrictors onto household services could also reduce overall water demand and therefore allow the water system to stay pressurized. Instead of a system that allowed “maximum water quantity,” a water utility could allow a fixed water quantity, a set amount per day regulated through a flow restrictor. This would reduce overall water demand and allow systems to stay pressurized, and hence facilitate continuous water supply and avoid interruptions. It is clear that a demand management strategy should be an integral part of the policy of eliminating IWS and replacing it with continuous water supply.

Some trickle fill systems in Alberta and Ontario

Drinking water trickle fill systems have been implemented in multiple places throughout Alberta including in Kneehill, Wheatland, Newell, Stettler, Starland, Lacombe, Lethbridge, and Cypress Counties. In approximately 20% (15 out of 72) of the rural counties and districts in Alberta, residents have connected to regional systems by implementing   the   trickle   fill   design  (Roulston,  2017; Alberta Municipal Affairs, 2017). The Province of Alberta (Canada) continues to be a good candidate for using trickle fill as a way of optimizing the use of existing water treatment plant capacities, which tend to be “over-dimensioned” in order to meet peak water demands in the high summer when drought conditions are possible.  As shown in Janzen et al. (2022), Alberta has a good network of main regional transmission pipes, with adequate pressure and uninterrupted power supply.

A similar trickle fill system also exists in Carlsbad Springs, in the rural outskirts of the City of Ottawa, which uses treated water from the City of Ottawa from a single watermain (Figure 6). The HDPE pipe used was of 2-inch diameter and no provision was made for firefighting. The original design was for 775 individual connections in the trickle fill system. While the majority of the connections supply water to single family homes, the capacity of the system allowed for a small number of large water users, such as a school, a hotel, a residential complex for seniors, a small apartment building, a golf course, and a recovery centre. As a result, the system was designed to accommodate a total of 829 “equivalent units”, each limited to a tank re?supply rate of 2.7 m³/day. No provisions were made for any growth beyond the 829 equivalent units (Ottawa City Infrastructure Policy Group, 2014).

The South Pacific Island country of Kiribati (Albetis and Lenehan 2003) and South Africa also have trickle fill systems in use (Scott and Tipping, 2001). The Carlsbad Trickle  Feed  System  is  perhaps  one  of  the  largest in Canada. Its continuing success demonstrates not only the technical feasibility but also indicates social acceptance of trickle fill systems in provinces as diverse as Alberta and Ontario. Their success indicates that there is an existing knowledge base regarding the development and operation of trickle fill systems.

Hence, countries where an existing intermittent water supply is in a reasonably good state of repair and has adequate pressure, or where an upgrading pumping station either exists or is planned, could consider the use of a Trickle Fill Water Supply System, using the existing network as a nucleus.

Evidence of trickle fill systems in Vietnam

It should also be noted that a version of trickle fill already exists in the city of Hanoi, but with a slight difference. In Hanoi the trunk pipes have lower pressure (10 m, or 98.7 kPa), which is about one-third of the average pressure in US water treatment pipes (Derrible et al., 2022).

However, the cisterns in the Hanoi residents’ homes fill up when the variable water supply and pressure are both available and are adequate. Hence, an adequate inventory of water is carried by the Hanoi households themselves. The cistern water can then be disinfected as and when required, using “point of use” filtration systems.

Incidentally, Vietnam is also innovating. Saldarriaga et al. (2020) report that the Hanoi reservoir, from which pipes emanate, has a constant pressure of 10 m (98.7 kPa), which is much lower than pressure in North American water networks. The whole Hanoi network comprises 34 pipes and 31 nodes configured in 3 loops.  Apart from Hanoi, the major cities of Vietnam all have successful water utilities.

In urban centres of Vietnam there is the possibility of using cisterns and flow restrictors to manage demand and reduce peak water usage, allowing systems to maintain continuous water supply. In rural areas there is a possibility of using trickle fill to supply water to areas where the groundwater wells have been contaminated. 

Given the availability of adequate electricity in Vietnam, all the remaining rural population could potentially receive continuous water supply through the implementation of a trickle fill system. That would accelerate Vietnam’s current water supply plans, and may be cost-saving. Of course, the actual implementation of any particular rural area is location specific and a pre-engineering assessment of a given rural population can be carried out by the tools and a template covered in Irwin (2018) and published in Janzen et al. (2022), which show free web access to the socio-economic, pre-engineering assessment tools. The decision-making tool incorporates three main aspects: (a) economic feasibility, (b) energy requirements, and (c) environmental impacts, which include the change in the carbon footprint. A detailed explanation on how the template can be used is made freely available by the authors, and may be accessed via the University of Calgary’s manuscript vault (Irwin, 2018) (https://prism.ucalgary.ca/handle/1880/109762).

Of course, before any actual investment occurs, the preliminary assessment must be followed with a site-specific engineering study to validate or refute any potential positive preliminary assessment.

The objective of this paper was to consider preconditions for expanding water infrastructure, improve access to drinking water and/or convert intermittent water supply to continuous water supply in homes and work places. Table 1 shows the problem of intermittent water supply was most severe in the (UN classified) Least Developed Countries. There are 39 countries under this classification. We considered a sample of 16 such countries with the objective of assessing their current capacity to make the transition to continuous water supply. These 16 countries have low per capita income and little or no foreign exchange that would be required to import, and no steel industry to manufacture locally, water infrastructure components, including water treatment plants, pumps and pipelines. Their plight is one of unsafe water and alarming numbers of associated deaths. They also do not yet have the electricity infrastructure that would be needed as a prerequisite for an extensive water network for continuous water supply. But before an engineering study is commissioned to build a water treatment plant, it is important to determine if the necessary finance is available to pay for it. When there is no domestic steel industry, it would be necessary to buy the treatment plant and pipes from abroad, that is, from a developed country supplier. That supplier will have to be paid in foreign currency. We know that foreign currencies are earned by exporting more than importing, or by maintaining a Current Account Surplus, or surpluses, to build up foreign reserves. For a developing country, it will be necessary to invest first in a “backbone” of water supply mains pipeline. This backbone can then be extended, by adding small diameter high- density polyethylene pipes that are called “trickle fill,” to maximize the utilization of the backbone of the network, which typically maintains good pressure. Thus, a trickle fill addition, coupled with a demand management strategy, could eliminate supply interruptions and achieve continuous water supply.

Some countries have successfully transitioned out of ‘least developed’ status and one such country is Vietnam. There is hope that soon at least some of the 16 countries will show enough income and export growth to leave “Least Developed” category. For example, Bangladesh and Cambodia, with strong and growing export performance over the next decade, could emulate the example of Vietnam.

As far back as 1986, Vietnam adopted the principles of a market economy, and embarked on a policy of export led growth. It has successfully raised loans, and established long term development plans to bring continuous water to the cities. For rural areas, it adopted a Rural Water and Sanitation Strategy for the delivery of continuous water supply to rural areas by 2030, and at least by 2045. But in 2021, some 4% of the rural population was without access to continuous and safe water. Of course, the government’s Rural Water Strategy Plan may include the usual approach to expanding water infrastructure, but in this paper, we suggest that an alternative lower cost approach be considered, and that alternative is Trickle Fill, in which existing pressurized pipes are connected to low diameter high density polyethylene pipes, with cisterns at the rural households, as in Hanoi, but extend it to other parts, mainly rural residents not too far from a water main. The Trickle fill solution, already adopted successfully in many parts of the world, would be worth considering not only in rural Vietnam, but also in other developing countries that have once invested in adequate electricity supply network. 

The authors have not declared any conflict of interests.