=Paper=
{{Paper
|id=Vol-2120/paper3
|storemode=property
|title=Measuring Surface Water Quality Using a Low-Cost Sensor Kit within the Context of Rural Africa
|pdfUrl=https://ceur-ws.org/Vol-2120/paper3.pdf
|volume=Vol-2120
|authors=Allard Oelen,Chris J. van Aart,Victor de Boer
|dblpUrl=https://dblp.org/rec/conf/websci/OelenAB18
}}
==Measuring Surface Water Quality Using a Low-Cost Sensor Kit within the Context of Rural Africa==
https://ceur-ws.org/Vol-2120/paper3.pdf
Measuring surface water quality using a low-cost sensor kit
within the context of rural Africa
Allard Oelen Chris van Aart Victor de Boer
Vrije Universiteit Amsterdam 2CoolMonkeys BV Vrije Universiteit Amsterdam
2CoolMonkeys BV Netherlands Netherlands
Netherlands chrisvanaart@2coolmonkeys.nl v.de.boer@vu.nl
a.b.oelen@vu.nl
ABSTRACT 1. What is an effective design of a low-cost water quality measuring
Monitoring water quality is done for a variety of reasons, including kit within the context of rural Africa?
to determine whether water is suitable for drinking or agricultural 1.1 What are the requirements and constraints of the system design
purposes. In rural areas of Africa the traditional way of measuring with respect to the context of rural Africa?
water quality can be costly and time consuming. In this research, 1.2 What are appropriate sensors to measure water quality for the
we have developed a low-cost water quality measuring device that measuring kit?
designed to operate in the context of rural Africa. Firstly we select
appropriate water quality sensors. Secondly we developed a water The meaning of the word effective in the first research question, is
quality monitoring device that takes the contextual requirements explained in more detail in the two subquestions. For the purpose
and constraints of rural Africa into account. Lastly the device is of our research, we define effectiveness as how well the system
evaluated and tested using water samples that were collected in conforms to the requirements and constraints. For example, if there
rural Africa. is no internet connection available, alternative methods for connec-
tivity should be included in the system design. Additionally, there
KEYWORDS is a trade-off between the building costs and measuring quality.
This also involves the selection of appropriate sensors. Sensors are
ICT4D, water quality monitoring, low-cost sensor kit, IoT4D
considered appropriate for this context, if they are low-cost and
still provide correct information about water quality parameters.
1 INTRODUCTION
Measuring surface water quality has been done for decades for a 2 RELATED LITERATURE
variety of reasons. Among those reasons are to find out whether
water is drinkable or if it can be used for agricultural purposes [2]. 2.1 ICT4D context
Traditional methods to determine water quality can be time con- In this research, we focus on implementing an ICT solution within
suming and expensive [9]. Water samples are sent to a laboratory rural Africa. This results in multiple requirements and constraints
and those samples are analyzed there. Using this method of water that are specifically related to this context. ICT research for devel-
analysis it is not possible to determine water quality ad hoc. For opment is called Information and Communication Technologies For
example in the context of rural Africa, a farmer wants to know if Development (ICT4D or ICTD). More specifically, ICT4D is defined
the water from the river can be used to water his or her crops. If the by Gyan as the use of ICT in socio-economic and international
farmer has to wait a few weeks to find out whether the water at that development. This includes disadvantaged population all over the
moment is suitable for watering crops, the results are not relevant world, but more often ICT4D is related to developing countries
anymore when they arrive. The water composition could have been [5]. Ali et al. mentions three benchmarks that are important for
changed since the samples were taken. A more suitable method of successful ICT4D projects: context, community participation and
determining the water quality would be a solution that provides sustainability. However, sustainability seems to be conflicting with
information about the water quality instantly. This device should ICT in general, which is changing often. Therefore Ali et al. quali-
be affordable from a financial perspective. Using such a device has fies sustainability of ICT4D projects as an unrealistic concept and
multiple advantages over traditional water quality measuring ap- that pursuing sustainability leads to project failures [1].
proach: water quality can be measured instantly, measurements can Implementing an ICT system within developing countries raises
be taken continuously and measuring can be done by stakeholders multiple challenges that are not obvious or present in first-world
itself instead of being dependent on a laboratory. A disadvantage countries. Users of ICT systems often have limited education, are
of using a low-cost sensor kit is that fewer water parameters can underemployed and have low incomes [12]. On the other hand,
be measured and these measures are potentially less accurate. stakeholders of such systems are from different countries and have
In this research, we will develop a low-cost water quality measur- different sociocultural backgrounds [13], which can complicate
ing device. This device (or sensor kit) is designed to function within determining the goals of a project. Pitula et al. described other
the context of rural Africa. This means that there will be various challenges of the complicated context in which ICT4D projects
requirements and constraints that are related to this context. To be operate, related to infrastructures, power supplies, connectivity and
able to develop the water quality measuring device, the following extreme operating conditions. Additionally three main components
research questions will be answered: of ICT4D projects are described: 1) infrastructure development,
2) create ICT capacity and 3) providing the digital service. The
first component relates to the required infrastructure to operate the measuring results. AKVO has developed a lens for a smartphone
the system. The second component relates to the capacity to use camera as well. With this lens it is possible to determine certain
and maintain the system. Finally, the third component relates to water quality parameters [10]. Using a smartphone, the prices of
the value of the service itself [13]. Because network connection sensors kits can decrease significantly. However, there are multiple
are extremely unreliable or not available at all in rural areas of downsides of method. The most obvious downside is that a smart-
developing countries, other techniques are used to make the web phone is needed (which is not always available, especially in rural
accessible. Research of Valkering et al. focuses on transmitting data areas of Africa). Additionally, this method is not very suitable for
via SMS in rural areas [19]. Most of the challenges listed above, monitoring water quality over a longer period of time (water qual-
are also relevant for our research. Solutions to overcome power ity cannot be measured autonomously). Our research differs from
and connectivity issues should be investigated in order to design a the previously discussed projects since we focus specifically on the
usable water quality measuring device for rural Africa. use in rural Africa. The measuring kit will not be dependent on a
According to Tongia et al. many ICT4D project fail either par- smartphone and is therefore suitable for autonomous continuous
tially or completely. This is caused by a incomplete problem defi- water quality monitoring.
nition or by the metrics used for evaluation [17]. Other research
confirms that most ICT systems for development do indeed fail 3 METHODOLOGY
[6, 13]. Among the reasons for failure is a gap between the design
of the system and the reality. The findings of the previously men-
3.1 Water quality parameter selection
tioned researches are relevant for our research. It indicates that the In order to design the water quality measuring kit, water quality
ICT4D context should be taken into account in both the system parameters are selected together with the appropriate sensors to
design phase and other phases (like the evaluation phase) in order measure these parameters. The parameters are selected based on
to succeed in this context. their relevance in rural Africa. This means that parameters that are
hard to measure (because of a high sensor price or a complicated
2.2 Water quality measurement procedure) are not included in this research. The parameters do pro-
Water quality can be determined using the physical, chemical and vide information about the quality of surface water. The selection
biological properties of water [18]. The Environmental Protection of the parameters has been done using a literature review. The final
Agency of Ireland described 101 parameters to determine water result of selecting water quality parameters is a table that contains
quality. Below a selection of those parameters are listed and cate- information about each individual parameter.
gorized by the previously mentioned quality property categories.
Firstly, physical parameters include for example: pH and tempera- 3.2 Measuring kit design and development
ture. Secondly, chemical parameters include: dissolved oxygen and Based on the table of water quality parameters, the appropriate
other measures of how much of a certain substance is present in sensors have been selected. The measurement device is using an
water. Lastly, biological properties include measures of bacteria and Arduino micro controller unit (MCU) to control the sensors. We
viruses (e.g. salmonella) [16]. The listed properties are relevant for have chosen for Arduino because it is an inexpensive and open-
this research because they can be measured using low-cost sensors. source I/O board that is often used for prototyping [3]. Additionally,
A study of Rao et al. describes a low-costs water monitoring sys- the availability of analog I/O pins is convenient for reading analog
tem that is measuring some of the parameters that were described values from various (water) sensors.
earlier. This includes temperature, pH, electrical conductivity and The development of the kit includes research into the most ap-
dissolved oxygen [14]. The findings of Rao et al. are relevant for this propriate power source, housing and communication method with
research since they also involve building a low-cost water quality respect to the context of rural Africa. As has been described in
measuring system. the related literature section, multiple challenging factors should
For amateur aquaponics and gardening, water quality monitoring be taken into account during the system development. To be able
often happens using low-cost sensor kits 1 2 . These sensor are often to find out how these constraints affect the design of the kit, the
controlled by Arduino prototyping boards. Due to the open-source constraints are listed together with possible design options. A list
nature of these projects, multiple tutorials are published online by of design options is shown below. This list is based on challenges
the Arduino community. These amateur projects can be interesting found by Pitula et al. [13].
to our research since the same goal is pursued: measuring water • Power supply: power net, battery, solar panels, smartphone
quality with cheap sensors. Although the goal is the same, the battery
environment in which the device operates is different. • Connectivity: using smartphone app, GPRS, LoRa, SMS,
A Dutch NGO called AKVO is focusing on measuring water qual- save on SD card
ity in a cost effective way using smartphones 3 . They use multiple • Communication: using smartphone app, LCD screen, web
methods in order to determine the quality, for example test strips interface
are used to measure certain parameters. The smartphone camera is • Operating conditions: waterproof housing, industrial sen-
then used to photograph the test strip in order to capture and store sor, lab sensors
1 https://kijanigrows.com/
2 https://www.cooking-hacks.com/documentation/tutorials/open-aquarium-
In the following sections, two different types of usage scenarios
aquaponics-fish-tank-monitoring-arduino/ are being described. The system requirements and constraints are
3 https://akvo.org/products/akvo-caddisfly/ determined based on these scenarios.
2
3.2.1 Water quality measurement on demand. The water qual- for a system that is low-cost, but still provides relevant information
ity kit is designed to be used on demand. This means that when about water quality. Depending on the usage scenario of the system,
someone wants to know certain water quality parameters, he or some design options could be in favor of others. The evaluation
she takes a sample of the water and puts in inside a cup. Afterwards provides a clear overview of what design decisions were taken dur-
the sensors of the measuring kit are also placed in the cup to mea- ing the development of the kit, and what other design options are
sure the water quality. Using the measuring kit using this method available. Since this research is still work in progress, the design
has implications for the system design. Firstly, powering the kit decisions are not extensively discussed in the results. This will be
becomes less of an issue since the kit could be powered by the user done at a later stage of the research.
(e.g. via a smartphone or a power bank). Secondly, connectivity
and communication can also be handled via the smartphone. Lastly, 4 RESULTS
more (expensive) sensors could be connected to the kit because 4.1 Water quality parameters
it will not be left unattended. In contrast to the continuous mea-
suring scenario (that will be discussed in the next section) fewer In Appendix A a table can be found with a list of six water quality
sensors kits have to be created to be effective and that is another parameters that are useful for this research. In this table the pa-
reason why sensor pricing is less of an issue. A disadvantage of this rameters are listed together with a description and a standard for
method, is that most water quality parameters are only relevant if drinking water. These standards come from both the United States
measured for a longer period of time (like temperature, dissolved Environmental Protection Agency (EPA) and the World Health Or-
oxygen and oxidation reduction potential). This means that their ganization (WHO). Some of the parameters provide clear safety
value itself (without the ability to measure changes) is not very range for drinking water. For example, water with a pH below 6.5
helpful in determining water quality. A continuous water quality should not be drunk. But a parameter like temperature does by
measuring approach would overcome this problem. itself not provide information about whether the water is drinkable
or not. A bottle of water that has been heated by the sun can still be
3.2.2 Continuous autonomous water quality measurement. In perfectly drinkable. However, when measured for a longer period
contrast to measuring on demand, it is possible to do continues of time, monitoring the water temperature can provide helpful in-
measurements. Multiple sensor kits will be placed at different lo- sights into the water quality. The final parameter list is composed
cations and they will constantly collect information about water based on existing literature of research concerning water quality
quality. This is done using an Internet of Things (IoT) approach, measurement [8, 14, 15, 18, 20]. According to Tuna et al. the fol-
which will connect the sensors to the internet. This has implications lowing parameters are main parameters to measure water quality:
on the system design, including questions regarding: how to power electrical conductivity, dissolved oxygen, nitrate, pH, temperature,
the system, how to communicate the data to the stakeholders and turbidity.
how to handle connectivity? Possible answers to these questions
are: using solar power, communicate data via a web Graphical User 4.2 Development of the device
Interface (GUI), connectivity via GPRS. Additionally, the pricing of 4.2.1 First iteration. The water quality kit of the first iteration
the sensor kit becomes more important since the kits can be stolen has been shipped to Mali for testing in the field. This prototype
or damaged and because multiple sensor kits have to be created. contained the following sensors: temperature, turbidity, pH and
TDS. In Table 1 a more detailed overview of the specific sensors
3.3 Testing and evaluation and hardware of this device is listed. The housing of the device has
The device is built in multiple iterations. The first prototype has been printed using a Ultimaker 3D printer. The total price of the
been shipped to rural Africa. The testing phase is focusing on mul- kit is around 200USD. The price can be reduced by replacing the
tiple factors. Firstly, the sensors are tested to find out whether they solar power bank, by a self built solar charging system (which has
provide accurate information about water quality. This testing is been done in iteration two).
done using water samples collected from Ghana and Burkina Faso.
Table 1: Hardware specification of first iteration device
Testing in a real life setting is done in The Netherlands. The sensor
kit is placed at several rivers, lakes and canals. This is done both for
Type Description Costs
testing the sensors and to test and evaluate overall system design.
Haoshi H-101 Industrial pH sensor $56.95
In the end, the evaluation of the system focuses on answering the Development board for sensor con-
Linkit One $59.00
research questions that were stated in section one. This includes trol
an answer to the first research question: What is an effective design DFRobot
of a low-cost water quality measuring kit within the context of rural analog TDS TDS sensor $12.90
Africa?. An answer is provided by the description of an effective sensor
design. This is done by evaluating the requirements and by testing DS18B20 Temperature sensor $6.90
different design option available to fulfill these requirements. An TSD-10 Turbidity sensor $9.90
effective system should be able to correctly measure water qual- Xtorm Magma 3000 mAh solar power bank $50.00
ity parameters and make some conclusion about the actual water
quality. In the evaluation the trade-off between building costs and The device can operate both as "water quality tool on demand"
measuring quality is explained. An optimal solution is determined or as "continuous autonomous water quality monitoring tool" (the
3
two use cases described in section 3.2). For the first use case, a LCD
screen on the device displays water quality parameters in real time.
For the second use case, the data is sent to a server. The sensors
were controlled with a Linkit One4 . This device runs the same code
as Arduino, but has multiple connectivity options built in. Among
other things, GPRS and GPS are included. GPRS is used to send the
sensors data, time and location to a server. GPS is used to determine
the current location of the device. The device operates as follows:
(1) Set up device (connect sensors, turn on solar panel)
(2) Put the sensors in the water
(3) Water quality parameters appear on LCD screen. LCD back-
ground is green if the parameters are in a safe range, the
background becomes red if values are outside the safe range
Figure 2: Prototype of autonomous second iteration device
(4) Water quality parameters and location are sent to the server
4.4 Water quality data
The first iteration device did collect data from a well in Burkina Faso.
The second iteration device has not been shipped to rural Africa,
but has been tested in The Netherlands. This device is used to deter-
mine the quality of water samples that were collected at multiple
locations in rural Africa. The collected data is publicly available, via:
[11]. For the first iteration device that was tested in Burkina Faso,
all measured values were within the safety range. However, some
water samples that were tested using the second iteration device,
did have a pH value that was below the EPA guideline (below pH
Figure 1: Block diagram of first iteration device 6.5).
4.2.2 Second iteration. The second iteration of the device is
currently being constructed. This iteration focuses on adding more
sensors and on improving the construction of the device itself.
Among the new sensors is an ORP sensor. When the first iteration
device was shipped to rural Africa, some internal wires came loose.
The second generation device will therefore be more robust to
prevent this from happening. In this second iteration, two separate
devices will be constructed. This is done in order to fulfill the
requirements that are specific for the two use cases described in
section 3.2. One device will be used to measure water quality on
demand (an LCD screen will be used to communicate the sensor data
to the user). The other device is made for continues water quality
measurement, this means that the device has to be waterproof and
it should work autonomously. No LCD screen will be connected to
this device, sensor data is sent directly to the cloud. Figure 2 depicts
a prototype of the device.
4.3 Online interface
The online interface displays the data that the device has sent to
server. Using the time range selector, it is possible to monitor and
compare water quality parameters over time. The map shows the
location of where the device was used to measure water quality.
The source code of the program can be found online5 . Figure 3
shows a screenshot of how the interface looks like.
4 http://wiki.seeedstudio.com/LinkIt_ONE/
5 https://github.com/aoelen/compteur-deau Figure 3: Online interface screenshot
4
5 DISCUSSION well. For example, it is possible to develop low-cost weather stations
This research is still work in progress. We expect to add more sen- using a similar setup as presented in this research. The sensors
sors in a later stage. Some hardware changes will be made to make would be different, but many of the requirements and design options
the device more robust, and to make it better suitable for moni- are the same. Another interesting research topic would be reusing
toring over a longer period of time. Additionally, a more detailed old computer hardware. For example, computers have multiple
evaluation of the design decisions will be added. sensors for measuring temperature, research could focus on how
to reuse such sensors in similar projects.
5.1 Device usage
REFERENCES
The first prototype has been shipped a rural Africa. The device
[1] Maryam Ali and Savita Bailur. 2007. The Challenge of " Sustainability " in ICT4D
was used by a researcher to measure the water quality at a certain - Is Bricolage the Answer ? Proceedings of the 9th International Conference on
location. After the researcher left, the device was given as a present Social Implications of Computers in Developing Coutries 29, May (2007), 54–60.
[2] S. R. Carpenter, N. F. Caraco, D. L. Correll, R. W.Howarth, A. N. Sharpley, and
to the locals. The device could have been used by them, to test V. H. Smith. 1998. Nonpoint pollution of surface waters with phosphorus and
the quality of different water sources. However, we did not receive nitrogen. Ecological Applications 8, 1998 (1998), 559–568. https://doi.org/10.1890/
any data from the device, which is an indication that the device 1051-0761(1998)008[0559:NPOSWW]2.0.CO;2
[3] Alessandro D’Ausilio. 2012. Arduino: A low-cost multipurpose lab equip-
is not used anymore. Therefore, one can question whether the ment. Behavior Research Methods 44, 2 (2012), 305–313. https://doi.org/10.
water quality on demand use case, is a realistic scenario. In the 3758/s13428-011-0163-z
end, such a device can never give a definitive result about whether [4] H G Gorchev and G Ozolins. 2011. WHO guidelines for drinking-water quality.
WHO chronicle 38, 3 (2011), 104–108. https://doi.org/10.1016/S1462-0758(00)
the water is drinkable or not. This means that using the device on 00006-6
demand is less interesting to locals. The device is still useful for [5] Nana Baah Gyan. 2016. The Web, Speech Technologies and Rural Development
in West Africa. (2016).
monitoring water quality over a longer period of time. The device [6] Richard Heeks. 2002. Failure, Success and Improvisation of Information Systems
in this scenario works autonomously, and therefore the previously Projects in Developing Countries. Development 32, University of Manchester
described difficulty does not apply. (2002), 45. https://doi.org/10.1016/0736-5853(84)90003-0
[7] Cn James, Rc Copeland, and Da Lytle. 2004. Relationships between oxidation-
reduction potential, oxidant, and pH in drinking water. Proceedings of the AWWA
5.2 Sustainability Water Quality Technology Conference (2004), 1–13. https://cfpub.epa.gov/si/si_
public_file_download.cfm?p_download_id=460980
As has been described in the related literature section, sustainability [8] Peng Jiang, Hongbo Xia, Zhiye He, and Zheming Wang. 2009. Design of a water
of ICT4D projects is often used as benchmark to measure project environment monitoring system based on wireless sensor networks. Sensors 9, 8
(2009), 6411–6434. https://doi.org/10.3390/s90806411
success. A full sustainability study is out of scope for this research, [9] James W. Kirchner, Xiahong Feng, Colin Neal, and Alice J. Robson. 2004. The fine
however since sustainability is a crucial success factor of ICT4D structure of water-quality dynamics: The (high-frequency) wave of the future.
projects we will discuss some aspects of this subject. Both the hard- Hydrological Processes 18, 7 (2004), 1353–1359. https://doi.org/10.1002/hyp.5537
[10] Saurabh Levin, Sunderrajan Krishnan, Samuel Rajkumar, Nischal Halery, and
ware and software of the device are open-source. Open-source for Pradeep Balkunde. 2016. Monitoring of fluoride in water samples using a
ICT4D projects has multiple advantages. With the respect to the smartphone. Science of the Total Environment 551-552 (2016), 101–107. https:
hardware, the advantage is that parts can be replaced with other //doi.org/10.1016/j.scitotenv.2016.01.156
[11] Allard Oelen. 2018. ICT4D Water quality measurement device - Data. https:
(similar) hardware without the help of the product developers. This //doi.org/10.6084/m9.figshare.6142811.v1
is useful in multiple situations, e.g. if certain components break or if [12] T.S. Parikh and D.E. Lazowska. 2006. Designing an Architecture for Delivering
Mobile Information Services to the Rural Developing World. Proceedings of
someone wants to extent the system. For some sensors a BNC con- the 15th international Conference on World Wide Web (2006), 791–800. https:
nector has been used. This means that when a sensor probe stops //doi.org/10.1109/WMCSA.2006.7
working, it is possible to replace this probe by a sensor with the [13] Kristina Pitula and Deborah Dysart-Gale. 2010. Expanding the Boundaries of HCI
: A Case Study in Requirements Engineering for ICT4D. Information Technologies
same BNC connection. Since this connection is a common standard, & International development 6, 1 (2010), 78–93. http://itidjournal.org/itid/article/
no internal parts need to be replaced. Additionally, the open-source view/491/216
software also ensures that the system can be expanded or adjusted [14] A.S. Rao, S. Marshall, J. Gubbi, M. Palaniswami, R. Sinnott, and V. Pettigrovet. 2013.
Design of low-cost autonomous water quality monitoring system. Proceedings of
by any stakeholder. In the end, by using and providing open-source the 2013 International Conference on Advances in Computing, Communications and
hardware and software, we ensure that the original device develop- Informatics, ICACCI 2013 (2013). https://doi.org/10.1109/ICACCI.2013.6637139
[15] Zulhani Rasin and Mohd Rizal Abdullah. 2009. Water Quality Monitoring System
ers do not have an crucial role for system operation. This benefits Using Zigbee Based Wireless Sensor Network. International Journal of Engineering
the overall sustainability of the water quality measuring device. & Technology 9, 10 (2009), 14–18.
[16] The Environmental and Protection Agency. 2001. Parameters of water quality.
Environmental Protection (2001), 133. https://doi.org/10.1017/CBO9781107415324.
5.3 Future work 004
Only the first iteration device has been shipped to rural Africa. In [17] Rahul Tongia and Eswaran Subrahmanian. 2006. Information and Commu-
nications Technology for Development (ICT4D) A Design Challenge? 2006
order to ensure that the device is useful and capable for long-term International Conference on Information and Communication Technologies and
operation, more devices should be tested in rural areas. Future Development 202 (2006), 243–255. https://doi.org/10.1109/ICTD.2006.301862
[18] Gurkan Tuna, Orhan Arkoc, and Kayhan Gulez. 2013. Continuous monitoring of
research could focus on the actual deployment of the water quality water quality using portable and low-cost approaches. International Journal of
measuring device. The feedback from stakeholders and the collected Distributed Sensor Networks 2013 (2013). https://doi.org/10.1155/2013/249598
sensor data from the device, can be used to evaluate the device and [19] Onno Valkering. 2016. Knowledge Engineering and Knowledge Management.
10024 (2016), 697–712. https://doi.org/10.1007/978-3-319-49004-5
to improve the overall system design. [20] N Vijayakumar and R Ramya. 2015. The real time monitoring of water quality in
In this research, we focused on using low-cost sensors to measure IoT environment. 2015 International Conference on Circuits, Power and Computing
and monitor parameters specific to water quality. Low-cost sensor Technologies [ICCPCT-2015] (2015), 1–4. https://doi.org/10.1109/ICCPCT.2015.
7159459
kits can be useful for other applications in the ICT4D context as
5
A LIST OF WATER QUALITY PARAMETERS
Drinking water stan-
Parameter Description Reference
dard
Parameter to measure the total amount
Total Dissolved Solids of dissolved solids. A higher TDS might <600 mg/l
WHO [4]
(TDS) be an indication of pollution in the wa-
ter.
The amount of oxygen that is dissolved
in the water. Low levels of dissolved oxy-
Dissolved oxygen (DO) gen can be due to high water tempera- No guideline EPA6
tures or can be indicative for bacteria in
the water.
The ability of water to either accept or
Oxidation Reduction NSW7 ; EPA
release electrons. Bacteria are killed by No guideline
Potential (ORP) [7]
increasing the ORP level.
Measure to determine whether the wa-
ter is acidic (pH <7) or basic (pH >7). 6.5