Surveillance
5.3 Adequacy of supply
As the drinking-water supply surveillance agency has an interest in the population at large, its interest extends beyond water quality in isolation to include all aspects of the adequacy of drinking-water supply for the protection of public health.
In undertaking an assessment of the adequacy of the drinking-water supply, the following basic service parameters of a drinking-water supply should normally be taken into consideration:
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Accessibility: the percentage of the population that has reasonable access to an improved drinking-water supply;•
Quantity: the proportion of the population with access to different levels of drinking-water supply (inadequate access, basic access, intermediate access, op- timal access) as a proxy for the quantity of water used;•
Quality: whether the supply has regularly verified water quality and an approved WSP (see chapter 4) that has been validated and is subject to periodic audit to demonstrate compliance with relevant regulations (see chapters 3 and 4);•
Continuity: the percentage of the time during which drinking-water is available (daily, weekly and seasonally);•
Affordability: the price of water paid by domestic consumers.As the assessment of the quality of drinking-water is covered extensively through- out the Guidelines, including in section 5.5.2, this section focuses on the other basic service parameters.
5.3.1 Accessibility
From the public health standpoint, the proportion of the population with sustained, reliable access to safe drinking-water is the most important single indicator of the overall success of a drinking-water supply programme.
There are a number of definitions of access (or coverage), many with qualifica- tions regarding safety or adequacy. Sustainable Development Goal (SDG) target 6.1 calls for universal and equitable access to safe and affordable drinking-water for all.
The target is monitored using the indicator “proportion of population using safely managed drinking water services”, which is defined as the use of an improved water source that is accessible on premises, available when needed, and free from faecal and priority chemical contamination (WHO & UNICEF, 2017). SDG target 1.4 also references drinking-water, by calling for “all men and women” to have equal access to
basic services, including “basic drinking water services”, which are defined as use of an improved water source, provided that collection time is not more than 30 minutes for a round trip, including queuing.
An improved drinking-water source is one that has the potential to deliver safe water by the nature of its construction and design. Improved sources are more likely than unimproved sources to supply drinking-water free from microbiological con- tamination, although microbiological contamination does occur in all types of water supply, particularly when they are inadequately managed. Improved and unimproved water supply technologies are summarized below:
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Improved drinking-water sources:— piped supplies (including household and yard connections, public taps and standpipes)
— boreholes and tubewells
— protected dug wells
— protected springs
— rainwater
— water kiosks
— packaged water
— delivered water.
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Unimproved drinking-water sources:— unprotected dug wells
— unprotected springs
— surface water (rivers, reservoirs, lakes, ponds, streams, canals and irrigation channels).
Determining the proportion of a population with reliable access to drinking- water is an important function of a drinking-water surveillance agency. This task can be facilitated by establishing a common definition for reasonable access, appropriate to the local context, which may describe a minimum quantity of water supplied per person per day, together with a maximum tolerable distance or time to a source (see section 5.3.2).
The global SDG indicators identify different levels of accessibility: the basic ser- vice indicator calls for improved water supplies to be located within a 30-minute round trip travel time, including queuing, while the safely managed services indica- tor requires that the water collection point be located on-premises (i.e. within the household, yard or plot).
5.3.2 Quantity
The quantity of water used by households has an important influence on health.
There is a basic human physiological requirement for water to maintain adequate hydration and an additional requirement for food preparation. There is a further requirement for water to support hygiene, both personal and household, which is necessary for health.
Estimates of the volume of water needed for health purposes vary widely. In deriving World Health Organization (WHO) guideline values, it is assumed that the
Table 5.1 Summary of water access, adequacy and level of health concern Access
level Distance/time Likely volumes of
water collected Public health risk
from poor hygiene Intervention priority and actions Inadequate
access
More than 1 km or more than 30 min total collection time
Very low: can be below minimum daily requirements for hydration
Very high Hygiene practice compromised Basic consumption may be
compromised
Very high Provision of safely managed water at least to intermediate access Hygiene education Basic access 100 m to 1 km or
5–30 min total collection time
Average quantity unlikely to exceed 20 litres per person per day
High
Hygiene may be compromised Laundry and bathing may occur off‑plot
High
Provision of safely managed water at least to intermediate access Hygiene education Intermediate
access Water provided on‑plot through at least one tap, or within 100 m or 5 min total collection time
Average quantity approximately 50 litres per person per day
Medium Personal hygiene should not be compromised under usual conditions but may be compromised under outbreak conditions
Medium
Hygiene promotion still yields health gains Encourage optimal access
Optimal
access Supply of water through multiple taps within the house
Average quanity will exceed 100 litres per person per day
Low
Personal hygiene should not be compromised Household cleaning is also likely assured
Low
Hygiene promotion still yields health gains
Source: Domestic water quantity, service level and health, 2nd edition (supporting document in Annex 1)
daily per capita consumption of drinking-water is approximately 2 litres for adults, although actual consumption varies according to climate, activity level and diet.
Based on currently available data, a minimum volume of 5.3 litres per person per day will provide sufficient water for hydration under most conditions. There is insuf- ficient empirical evidence to define a minimum quantity of water necessary for food preparation or for hygiene. Experience and expert opinion suggest that 20 litres per person per day is often sufficient for drinking, cooking, food hygiene, handwashing and face washing. However other hygiene practices, including bathing and laundry, may not be assured. Further, where demands for water are increased—for example, due to increased hand hygiene in response to outbreaks of disease—20 litres per per- son per day may be insufficient; in many cases, running water from a tap will be necessary to support sufficient handwashing.
The quantity of water collected and used by households is primarily a function of the distance to the water supply or the total collection time required (including queuing). This broadly equates to access level. Four levels of access can be defined, as shown in Table 5.1.
Access level is a useful and easily measured indicator that provides a valid proxy for the quantity of water collected by households and is the preferred indicator for surveillance. Available evidence indicates that health gains accrue from improving access level in three key stages: delivery of water within 1 km or 5–30 minutes of total collection time (“basic access”); water being supplied reliably on-plot, espe- cially when running water is available (“intermediate access”); and water being avail- able within the home through multiple taps (“optimal access”). The first and second categories of access broadly align with the access levels associated with basic and safely managed services, respectively. Although health gains do occur in these two categories, health concerns remain, particularly during outbreaks of disease when enhanced personal hygiene is needed. The volume of water collected may also de- pend on the continuity, reliability and cost of the water. Therefore, collection of data on these indicators is important.
5.3.3 Continuity
Interruptions to drinking-water supply, as a result of either intermittent sources or engineering inefficiencies, are a major determinant of the quantity and quality of drinking-water available to households. Analysis of data on continuity of supply re- quires the consideration of several components. Continuity can be classified as follows:
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year-round service from a reliable source with no interruption of flow at the tap or source;•
year-round service with frequent (daily or weekly) interruptions, of which the most common causes are:— water production that is insufficient to meet demand, requiring rationing of water;
— restricted pumping regimes in pumped systems, whether planned or due to power failure or sporadic failure;
— peak demand exceeding the flow capacity of the transmission mains or the capacity of the reservoir;
— excessive leakage within the distribution system;
— excessive demands on community-managed point sources;
— breakdown of components of point sources (e.g. handpump parts);
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seasonal service variation resulting from source water fluctuation, which typi- cally has three causes:— natural variation in source water volume during the year, which may be exac- erbated by changes in climate (see section 6.1);
— volume limitation because of competition with other uses, such as irriga- tion;
— periods of high turbidity when the source water may be untreatable;
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combined frequent and seasonal discontinuity.These classifications reflect broad categories of continuity, which are likely to af- fect the quantity and quality of water available and thereby public health in different ways. Any interruption of service is likely to result in an increased risk of degrada- tion of water quality, an increased risk of exposure to contaminated water and there-
fore an increased risk of waterborne disease. Managed discontinuity often results in low supply pressure and a consequent risk of in-pipe recontamination. Other con- sequences include reduced availability and lower volume use, which adversely affect hygiene. This may be a problem both when the discontinuity is predictable and when it is highly unpredictable. Household water storage may be necessary, and this may lead to an increase in the risk of contamination during such storage and associated handling. Discontinuity often forces users to obtain water from inferior and distant sources. As a consequence, in addition to the obvious reduction in water quality and quantity, time is lost in water collection, and other risks (e.g. to musculoskeletal health) may arise. This applies particularly to women, who disproportionately bear the burden of collecting and hauling water from off-premises sources.
The SDGs do not specify a minimum quantity of water to be available, but the safely managed drinking-water services indicator calls for water to be “available when needed”. For the purposes of global reporting, households are considered to have wa- ter available when needed if they report having “sufficient water” or that water is avail- able “most of the time” (i.e. at least 12 hours per day or 4 days per week). However, although this metric is useful for global monitoring, it does not imply that this level of continuity is sufficient to realize public health gains, or that it represents a norma- tive target. The indicators used for SDG monitoring are simplifications and do not capture all aspects of water services that are important from a normative perspective.
5.3.4 Affordability
Affordability, or economic accessibility, implies that individuals or households should be able to purchase water without compromising the purchase of any other basic needs (UNICEF & WHO, 2021). A critical component in assessing affordability is the cost of water paid by individuals and further information related to costs is de- scribed in these Guidelines.
The cost of water has an influence on the use of water and selection of water sources. Households with the lowest levels of access to safe water supply frequently pay more for their water than do households connected to a piped water system. The high cost of water may force households to use alternative sources of water of poorer quality that represent a greater risk to health, or to use multiple sources of water, which may have varying quality and therefore also pose a risk to health. Furthermore, high costs of water may reduce the volumes of water used by households, particularly where multiple sources are not available, which in turn may influence hygiene prac- tices and increase risks of disease transmission.
When assessing cost, it is important to collect data on the price at the point of purchase. Where households are connected to the drinking-water supplier, this will be the tariff applied. Where water is purchased from, for example, public standpipes or trucked water, the price at the point of purchase may be very different from the drinking-water supplier tariff. Many alternative water sources (notably vendors) also involve costs, and these costs should also be considered. In addition to recurrent costs, the costs for initial acquisition of a connection for households connected to the drinking-water supplier or where households have their own private point source should be considered.