Chapter Eleven: Metering

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1 Chapter Eleven:METERING


Water meters are used to measure the volume of water used in residential and commercial buildings that are supplied with water by a public water supply system. Water meters can also be used at the water source, well, or throughout a water system to determine its flow through a particular portion of the system. In most of the world water meters measure water flow in cubic metres (m3).


There are several types of water meters in common use. The choice depends on

  • the flow measurement method,
  • the type of end-user,
  • the required flow rates, and
  • accuracy requirements.

The following are the different types of water metres:

  • Displacement water meters
  • Velocity water meters

ο Multi-jet meters
ο Turbine meters
ο Compound meters

  • Electromagnetic meters
  • Ultrasonic meters
  • Prepaid water meters

Meters can be prepaid or post-paid, depending on the payment method. Most mechanical type water meters are of the post-paid type, as are electromagnetic and ultrasonic meters. With prepaid water meters, the user purchases and prepays for a given amount of water from a vending station. The amount of water credited is entered on media such as an IC or RF type card. The main difference is whether the card needs contact with the processing part of the prepaid water meter. In some areas, a prepaid water meter uses a keypad as the interface for inputting the water credit.


Prepaid water systems including water meters have attracted significant attention in Tanzania and they are considered to be game changer in ensuring sustainability of urban as well as selected rural water services in the country located in Kishapu, Karatu, Babati and Arusha. The management of these prepaid systems has covered over 1,400 villages (Human Development Innovation Fund (HDIF) Tanzania, 2019) and 23 out of 70 urban utilities (MoW, 2019) that are currently using the prepaid water metering as a means to improve revenue collection processes. Examples of urban utilities that have introduced pre-paid meters include IRUWASA, DAWASA, MWAUWASA and KASHWASA).The urban utilities have prioritized installation of prepaid water meters for big public consumers of water who have large debts for extended durations. On the other hand, most of small scale users in rural areas collect their water from water points that are fitted with pre-paid water metres.

Prepaid water refers to the situation where a consumer purchases water credit in the form of a prepaid water token in advance of getting the service. When the token is entered into the user interface unit (located in the user or consumer’s home).The token instructs the water management device to allow a certain amount of water through the meter before closing. Consumers can track usage, load credit remotely, and decrease the possibility of bill shock due to leakages or incorrect monitoring.


Different models of prepaid water meters are being piloted in various urban Water Supply and Sanitation Authorities (WSSAs) and in selected districts supported by Development Partners as well as in some CBWSO owned projects:



  • Prepaid water systems are an effective and efficient way of collecting water tariffs and they offer a high level of convenience to both the users and the local water supply authorities. They save time and do not require any paperwork. Moreover, the system eliminates cash transactions and therefore contributes to the transparency of tariff collection,
  • Prepaid metering reduces administration costs to a minimum, while removing the risk and frustration of late or non-payment of water bills,
  • Collecting data from prepaid meters is more efficient than the manual collection required for post-paid meters,
  • Prepaid water systems generate real-time data on water collection by users, tariffs collected from users, and water point functionality;
  • Prepaid systems are cost-effective solutions to sustainable water management in that they have a low cost of acquisition and, by curbing water usage; capital recovery is possible within months,
  • The water systems are able to distribute water equally, based on free water quotas, water balancing, and fluctuating demand,
  • Prepaid water metering gives consumers the opportunity to monitor their consumption and react immediately to possible leakages, thereby saving money.


It is important to understand two key aspects of prepaid water metering; prepaid water metering does not involve meters alone, but rather is a system; and three (3) major applications of prepaid technology which have different characteristics, impacts, and challenges. The notion of pre-payment metering obscures the complementary components of an integrated pre-payment system as illustrated by HDIF (2019), which includes:

  • The prepaid metering is a system that comprises metering, dispensing, and credit-loading components. The prepaid dispensing device is the technology required to load and transfer credit, a database recording customer purchase and metered consumption and on-going engagement with customers.
  • Prepaid water meters use a mechanical water meter, coupled to an electronics module with a credit meter and a water control valve. However, prepaid systems use rotating piston and Multijet water meters of which their accuracy can be easily affected by grit, sand, and air; and frequent supply interruptions raise the risk of malfunctioning.
  • The presence of the rotating piston and Multijet is a significant vulnerability for its metering systems especially in urban areas, where there are ageing networks, discontinuous supplies, and low-pressure fluctuations. Therefore, in such cases, the designers need to opt for electromagnetic and ultrasonic prepaid meters that are technically better suited to networks with supply interruptions. These models are also highly accurate; resilient to pressure changes, air, and grit; and have no moving parts.



Most of these facilities differ from one place to another. In the rural water utilities, the prepaid metering technology consists of the following (HDIF (2019):
(a) a water point, a kiosk (where the water point is,
(b) a shop,
(c) digital water tags,
(d) an application programming interface (API) for mobile money transfers,
(e) a database, and a dashboard for system monitoring and reports generation
(f) In another case, the system is a simple technology through which users can purchase credit using the water app on smartphones, through mobile money, or by receiving a remote gift via PayPal.
(g) Customers use a standpipe, kiosk or water point loads credit bought from designated vendors using a programmed metal key, a smartcard, or a keypad.
(h) Some prepaid systems do not support multiple taps, nor do they operate well when the water pressure is low, and on the other hand, some technology can handle multiple taps.
(i) In the case as (h) above, the utility must develop partnerships with technology providers in sustaining and scaling up the prepaid water meter systems. Among other things, this means agreeing on and enforcing software licensing agreements, protocols on data management and sharing and the use of future warranties; as well as understanding the technology provider’s role and responsibilities during and after the installation of prepaid water meters (including after-sale services by technology providers).


(a) As illustrated by HDIF (2019), customers use their own prepaid meters, and load credit using a tag, smartcard, or keypad.
(b) The tag, card, or code can only be used on the specific meter for which it is programmed.
(c) Once the credit is loaded into the meter memory, customers do not have to use the key each time they draw water.


As illustrated by HDIF (2019), commercial and institutional customers usually use the Prepaid Bulk flow meters where wide variation in flow can be expected, such as in multi-story business buildings, hospitals, schools, offices and other places where both low and high flows can occur due to several consumptions users.

These wide flow ranges are measured by using a built-in change-over valve together with small residential meters and large bulk meter. All bulk meters should be tested to ensure that they meet approved standards. The meter needs to be designed for far higher volumes than domestic meters and far greater accuracy, given the volumes. The large volumes of water sold to commercial and institutional customers comprise a significant source of income for water service providers in most urban towns.


Integration with post-paid revenue management is vital, supported by a database of meters and customers with records of consumption, credit purchases, and performance. This integration is more difficult and costly in terms of investment required (staffing and/or computer billing upgrades) or efficiencies foregone than is often assumed. Regular monitoring is required to track faults, exceptions, and real-time consumption against prepaid sales. Finally, making prepaid meters work and ensuring their acceptability requires consistent and sustained interaction with customers.


For accurate water flow measurements, the characteristics of the water flow have to be known, before a suitable meter type with the right specifications can be chosen to fulfil this task. The following aspects should be considered when selecting a suitable prepaid water meter:
(a) Assess the water quality: The water quality must comply with the one specified for a meter. Metering accuracy is significantly affected by suspended solids and depositions. Dirty water will cause under-registration with Positive Displacement as well as with Velocity Meters. Growth of algae in the meter can lead to blockage.
(b) Determine the consumption pattern (minimum and peak flow rates): Prepaid Water meter measures accurately only in flow rates that lie within its range of ability (Prepaid Meter accuracy should comply with ISO 4064:2014 Standards.
(i) Because domestic customers are large in numbers, it is recommended to make use of empirical field studies to analyze entire groups of domestic customers, e.g. those with or without storage tanks.
(ii) Commercial water user however, tend to follow a more individualized their consumption pattern and are worth to be assessed on an individual basis to determine his/her consumption pattern.
(iii) Also, the water supply network’s to be assessed in terms of pressure zones to determine whether the minimum and maximum are possible at all.
(c) Inaccuracy of wrongly sized meters
(i) When the prepaid water meter is too large the flow rates might be lower than the minimum flow rate and cause under-registration that will result in high non-revenue water. Also oversized meters are more costly than rightly sized meters.
(ii) Alternatively, when the prepaid water meter is too small it results in accelerated inaccuracy and high-pressure loss.
(iii) Undersized prepaid water meters can cause excessive pressure loss, reduced flow, noise and will eventually shorten its life span through wear and tear if operated frequently at or above its allowable maximum flow.
(d) Minimum and maximum pressure drop: should be within the meter specifications.
(e) The ordering of prepaid meter: is complete when they have in-line strainers to block debris to enter the metering unit. However, if a strainer needs to be installed it is recommended to install a backflow preventer (i.e. non-return valve as well).
Also, the following aspects should be considered when selecting a prepaid water meters:
(i) The piping conditions: are they new or existing network?
(ii) Assess available service and calibration service providers and costs e.g. Weights and Measures Agencies (WMA) etc
(iii) Availability of spare parts– if easily accessible in the local markets
(iv) Meter life span
(v) Costs of the prepaid meter integrated system (cheap or expensive)
(vi) Simplicity of the technology (software) used for prepaid metering system
(f) The correct specifications of the batteries used to power the unit. During procurement, it will be necessary to specify the minimum battery size to ensure they last for a long time.

REFERENCES Ministry of Water, The 3rd Edition Design Manual for Water supply and Wastewater Disposal, 2009.