International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
119
Potential for potable water and electricity savings by using
rainwater in central Mozambique
Helder P. de Carvalho1, Sergio C. de Placido2 and Prof. Jiguo Huang3
1
College of environmental engineering and natural resources, University Zambezi, Chimoio, Mozambique
(helarc2008@gmail.com)
2
Department of Earth Sciences, Universidade Pedagogica, Beira, Mozambique (splacido2007@yahoo.com.br)
3
Key Laboratory of Groundwater Resources and Environment, Ministry of Education, Jilin University, Changchun 130026, P.R.
China (helarc2006@yahoo.com.br)
Abstract
Nowadays, rainwater usage has been recommended to encourage potable water savings and minimize
water availability problems, due to the increasing number of population and socio-economic activities.
This paper describes the water availability scenario in central Mozambique, which is about 1500 m3 per
capita per year, but it is predicted to be lower than 200 m3 per capita per year from 2197 onwards. The
main objective of this paper is to estimate the potential for potable water savings by using rainwater in 4
capital cities located in central Mozambique. The potential for electricity savings in a water utility by
reducing potable water consumption in the residential sector are also evaluated. Results indicate that
average potential for potable water savings range from 0.44% to 164.53% for the capital cities analyzed,
with an average potential for potable water savings of 47%. The average potential for electricity savings
were 2.3 GWh/year, 1.6 GWh/year, 1.4 GWh/year and 0.4 GWh/year, respectively, for the city of Beira,
Quelimane, Chimoio and Tete. This study clearly shows that if there were a government programme to
encourage potable water savings by rainwater usage, there would be significant potable water savings and
a consequent preservation of water resources and electricity savings in central Mozambique.
IJSER
Keywords: Water availability; Potable water savings; electricity savings; Rainwater usage in central
Mozambique
1. Introduction
The increasing growth in population, industrialization and urbanization is causing severe impact over the
water resources [1]. It is already a reality in many countries (being the most critical countries like China
and India) and climate change will only accentuate the frequency and intensity of this problem in the
future. In order to ease water availability problems and decrease potable water demand, rainwater
harvesting has been suggested by many researchers [2]. Reports on this can be found in Herrmann and
Schmida [3], Coombes et al. [4], Fewkes [5], Marinoski et al. [6], Appan [7], Handia et al. [8], Li and
Gong [9], amongst others.
Rainwater harvesting is a simple low-cost technique that requires minimum specific expertise or
knowledge and offers many benefits. It is used in the richest and the poorest societies, as well as in the
wettest and the driest regions on our planet [10]. Rainwater is abundant in most parts of Mozambique,
especially in periods ranging from December to March. In the center region, which is composed of four
capital cities (namely Beira, Chimoio, Tete and Quelimane), average rainfall is 103 mm per year [11]. Fig.
1 shows rainfall data for four capital cities located in the center region of Mozambique for the period
1994 – 2013. Such data illustrate that there is significant amount of rainwater in the center region.
However, there is no government programme to promote rainwater harvesting. Nevertheless there are
some non-governmental organizations (such USAID – U.S. Agency for International Development and
Copyright © 2015 SciResPub.
IJOART
International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
120
IRD – International Relief and Development) that are starting to promote the collection of rainwater in
communities, with the main objectives of adds new sources of water and improve communities’water
management capacity and resilience to disasters. They are also contributing to ease a major problem of
water availability that has already begun to emerge in Mozambique and that will become critical in the
near future.
IJSER
Fig. 1. Average rainfall for four capital cities in central Mozambique over the period 1994 – 2013: (a) Beira – 175
mm per year; (b) Chimoio – mm per year; (c) Tete – mm per year; (d) Quelimane – mm per year.
Table 1 presents the total population, population served and unserved with potable water per each capital
city located in the center region of Mozambique for the period 2009 – 2013. Such data illustrate that
despite the considerable increase of the population served with potable water, still prevail a large number
of people without access to potable water. The most critical cases are registered in the city of Chimoio,
where the number of the population unserved with potable water exceeds the population served.
Table 1: Total population, population served and unserved with potable water per each capital city located in the center region of
Mozambique for the period 2009 – 2013
City
Beira
Chimoio
Tete
Year
2009
2010
2011
2012
2013
2009
2010
2011
2012
2013
2009
Total Population
526 805
539 448
552 395
565 652
579 228
255 397
264 847
274 646
212 313
Copyright © 2015 SciResPub.
Population served
361 652
428 521
490 798
514 897
520 234
44 799
45 325
85 541
71 840
Population unserved
165 153
110 928
61 597
50 755
58 192
210 598
219 522
189 105
140 473
IJOART
International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
2010
2011
2012
2013
2009
2010
Quelimane 2011
2012
2013
Source: FIPAG
221 655
231 408
241 590
252 220
204 719
210 656
216 765
223 052
229 521
118 458
178 824
207 889
224 733
145 103
157 611
171 370
166 163
157 779
121
103 197
52 583
33 700
67 203
59 616
53 045
45 396
56 889
71 741
Fig. 2 shows the population of central Mozambique for period 1987 – 2007 and the predicted population
for the period 2007 – 2197 taking into consideration the growth rate observed between 1987 and 2007
(corresponding to the first, second and third general census of population in Mozambique after the
independence). At the moment, there are more than 1.3 million people in central Mozambique; however
the predictions foresee that there will be more than 6.8 million people in the year 2197. On the other hand,
water availability, which is about 1500 m3 per capita per year at the moment, will be reduced to about 200
m3 per capita per year in the year 2197 (Fig. 2).
IJSER
Fig. 2. Population and water availability in central Mozambique from 1987 – 2197.
2. Objective
The main objective of this work is to evaluate the potential for potable water savings by using rainwater
in the residential sector of 4 capital cities located in the center region of Mozambique. The potential for
electricity savings in a water utility by reducing potable water consumption are also investigated.
3. Methodology
The methodology used to estimate the potential for potable water savings in central Mozambique is
similar to the one used by Ghisi et al. [12], which are necessary to obtain rainfall data, potable water
consumption, population and number of dwellings in each city. It was not possible to include all the
capital cities of Mozambique, because for now only the center region contains the required data. Fig. 3
shows a map of Mozambique indicating the location of the center region of the country.
Copyright © 2015 SciResPub.
IJOART
International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
122
Fig. 3. Map of Mozambique with location of the center region of the country and map of the center region with location of the 4
capital cities (displayed in red dots).
3.1. Rainfall data
Daily rainfall data were obtained from INAM [11]. When there were missing data, they were assumed to
be zero. The lack of data may be related to the interruption for maintenance, the breakdown of the
equipments or even by the lack of funding to keep all climatic stations in operation. The data were
processed in order to obtain the average monthly rainfall for each capital city.
IJSER
3.2. Potential for potable water savings
The potential for potable water savings by using rainwater in each of the 4 capital cities was calculated as
follows.
3.2.1. Population supplied with potable water and potable water demand
The number of people supplied with potable water and potable water demand in each capital city was
given by the water utility for the period 2009 – 2013. An arithmetic average was performed to obtain the
number of people supplied with potable water and potable water demand per month.
3.2.2. Number of people per dwelling
The number of people living in each capital city and the number of dwellings were obtained from INE
[13]. Thus the specific number of people per dwelling was estimated by using Eq. (1):
(1)
where PD is the number of people per dwelling, PC is the number of people living in the city, and NDC is
the number of dwellings in the city.
3.2.3. Number of dwellings supplied with potable water
The number of people supplied with potable water was obtained from FIPAG [14]. The number of
dwellings supplied with potable water was estimated by using Eq. (2).
,
Copyright © 2015 SciResPub.
(2)
IJOART
International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
123
where ND is the number of dwellings supplied with potable water, NP is the number of people supplied
with potable water per month (as given by the water utility company), and PD is the number of people per
dwelling.
3.2.4. Total roof area
From all dwellings located in central Mozambique, 97.6% on average are houses and 2.4% are flats
located in multi-storey residential buildings [13]. In order to obtain an average roof area in each capital
city, an average area of 85 m2 was assumed for houses and 50 m2 per person for flats. A weighted average
roof area per dwelling was then determined by using Eq. (3).
(3)
where RA is the weighted average roof area per dwelling in each capital city (m2), H is the percentage of
houses in each capital city (non-dimensional), F is the percentage of flats in each capital city (nondimensional), and PD is the number of people per dwelling in each capital city.
The total roof area in each capital city was obtained considering only the population supplied with potable
water. It was determined by using Eq. (4).
(4)
IJSER
where TRA is the total roof area in each capital city (m2), RA is the weighted average roof area per
dwelling in each capital city (m2), and ND is the number of dwellings supplied with potable water.
3.2.5. Volume of rainwater
The monthly volume of rainwater that could be harvested in each capital city was determined considering
monthly rainfall data, the total roof area, and a runoff coefficient of 0.8. Such a runoff coefficient
indicated a loss of 20% of the rainwater that is discarded for roof cleaning and evaporation. Thus, the
volume of rainwater that could be harvested in each capital city was determined by using Eq. (5).
,
(5)
where VR is the monthly volume of rainwater that could be harvested in each capital city (m3/month), R is
the monthly rainfall in each capital city (mm/month), TRA is the total roof area in each capital city (m2),
Rc is the runoff coefficient (non-dimensional), and 1000 is the conversion factor from litres to m3.
3.2.6. Potable water demand
The potable water demand considered in the analysis was determined as a function of the data obtained
from the water utility company for the period 2009–2013.
3.2.6. Potential for potable water savings
The monthly potential for potable water savings was determined for each of the 4 capital cities by using
Eq. (6).
,
(6)
where PPWS is the potential for potable water savings in each capital city (%), VR is the monthly volume
of rainwater that could be harvested in each capital city (m3/month), and PWD is the monthly potable
water demand in each capital city (m3/month).
Copyright © 2015 SciResPub.
IJOART
International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
124
3.3. Potential for electricity savings
In order to estimate the potential for electricity savings due to reduction of potable water demand by using
rainwater, indicators of the water utility company for the 4 capital cities (such as electricity consumption
for extraction, treatment and distribution of water) were used.
3.3.1. Potential for potable water savings
The potable for potable water savings (V) was determined as shown in section 3.2.5. An arithmetic
average was performed to determine the potential for potable water savings per year.
3.3.2. Potential for electricity savings
The potential for electricity savings due to the reduction of the water consumption (energy-savings with
extraction, treatment and distribution of potable water) was estimated by using Eq. (7).
(7)
where EE is the potential for electricity savings due to the reduction of water demand in each capital city
(kWh/year); V is the potential for potable water savings in each capital city as obtained in section 3.3.1
(m3/year); CE is the electricity consumption per m3 of water produced, obtained from FIPAG (kWh/m3)
[14].
IJSER
The electricity savings also correspond to financial savings due to reduction of operational costs for the
water utility company, determined by using Eq. (8).
(8)
where EF is the financial savings (MTn/year); EE is the potential for electricity savings due to reduction
of water demand in each capital city as obtained by using Eq. (7) (kWh/year); CEelectricity is the electricity
rate for the water utility company, obtained from EDM (MTn/kWh) [15].
In order to estimate the profit reduction to be faced by the water utility company due to the reduction of
water consumption, Eq. (9) was used.
(9)
where PR is the profit reduction (Mtn/ year); T is the average water rate, obtained from FIPAG (MTn/m3)
[14]; V is the potential for potable water savings in each capital city (m3/year).
4. Results
4.1. Number of people per dwelling
The number of people per dwelling ranged between 5.51 and 7.64 over the 4 capital cities, with an
average of 6.33 people per dwelling. Fig. 4 presents the results for the four cities.
Copyright © 2015 SciResPub.
IJOART
International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
125
Fig. 4. Number of people per dwelling over 4 capital cities in central Mozambique
4.2. Roof area
In order to determine an adequate roof area per dwelling, the percentage of houses and flats in multistorey residential buildings was obtained for the 4 capital cities. Such a distinction was deemed
appropriate as the specific roof area per person is lower in multi-storey buildings. Fig. 5 presents the
results for the 4 capital cities. The average indicates that 98% of all the dwellings are composed of houses
and 2% of flats in multi-storey buildings. Chimoio was the city with a high percentage of houses (99.5%),
but at the same time was the city with low average roof area (86.1 m2). While the city of Beira had high
percentage of flats in multi-storey residential buildings (6.2%) and high average roof area (98.8 m2).
IJSER
Fig. 5. Percentage of houses and flats in multi-storey residential buildings and average roof area in the 4 capital cities.
4.3. Potable water demand
Fig. 6 shows the potable water demand obtained for the 4 capital cities. It ranged from about 85 to 119
litres per capita per day. The average potable water demand obtained for the 4 capital cities was 93 litres
per capita per day.
Copyright © 2015 SciResPub.
IJOART
International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
126
Fig. 6. Potable water demand for the 4 capital cities.
4.4. Volume of rainwater
The monthly volume of rainwater that could be harvested in each one of the 4 capital cities was
determined through the procedure described in the methodology. Table 2 shows the results for the four
capital cities. It also presents the number of people per dwelling, potable water demand, average roof area
per dwelling and total roof area for the four capital cities.
IJSER
Table 2: Results for the four capital cities
Month
January
February
March
April
May
June
July
August
September
October
November
December
Number of
people per
dwelling
Potable
water
demand
(litres/capita
per day)
Average roof
area per
dwelling
(m2)
Total roof
area (m2)
Beira
Rainfall
(mm/month)
367
328
368
189
79
60
83
42
38
80
143
327
Volume
of
rainwater
(m3)
1164787
1043711
1169204
600849
250111
192148
263347
134772
121838
254052
455161
1039532
Chimoio
Rainfall
(mm/month)
252
173
134
60
17
13
17
12
32
56
67
150
Volume
of
rainwater
(m3)
213291
146704
113593
50883
14404
10608
14163
9825
27246
47773
56600
126736
Tete
Rainfall
(mm/month)
156
110
83
27
5
2
4
2
2
9
48
106
Volume
of
rainwater
(m3)
207109
145740
109523
35621
6379
3268
4671
2210
3282
11560
62924
140936
Quelimane
Rainfall
(mm/month)
323
219
196
114
56
50
73
22
12
20
45
156
Volume
of
rainwater
(m3)
311421
210929
189086
110163
53552
48101
69984
20841
11319
19554
43389
150063
6.15
6.02
7.64
5.51
99
68
118
85
99
86
89
88
3972290
1057863
1654335
1204706
Copyright © 2015 SciResPub.
IJOART
International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
127
4.5. Potential for potable water savings
The potential for potable water savings was estimated for the four capital cities and it ranged from 0.44%
in August to 160.53% in January. Fig. 7 shows the potential for potable water savings for the cities of
Beira, Chimoio, Tete and Quelimane observed for the 12 months. It can be observed that the potential for
potable water savings for the city of Beira from December to March, for the city of Chimoio in January
and for the city of Quelimane from January to February was above 100%. These results mean that for the
periods mentioned above, the volume of rainwater harvested can satisfy all the demand of the respective
cities.
IJSER
Fig. 7. Potential for potable water savings by using rainwater over the four capital cities.
4.6. Electricity savings
In order to estimate the electricity savings, some indicators of the water utility company for the 4 capital
cities were obtained from FIPAG [14] and are shown in Table 3.
Table 3: Indicators of the water utility company for the 4 capital cities obtained from FIPAG [14] and EDM [15] for the year
2013
Beira
Chimoio
Tete
Quelimane
Volume of water consumed in each capital city (1000 m3/year) 8796
1812
6024
2328
Electricity consumed per m3 of treated water (kWh/m3)
0.34
1.66
0.50
1.29
Electricity rates for the water utility company (MTn/kWh)
1.11
Table 4 presents the maximum potential for potable water savings and electricity savings. It can be
observed that the highest potential for potable water savings was obtained in the city of Beira, followed
by Quelimane, Chimoio and Tete. The highest and lowest potential for electricity savings 2274
MWh/year and 367 MWh/year (obtained for the city of Beira and Tete, respectively), which corresponds
to the electricity consumption of 94203 and 33020 dwellings with an average consumption of 190
MWh/month and 31 MWh/month in the city of Beira and Tete, respectively.
Table 4: Maximum potential for potable water savings and electricity savings for the four capital cities.
Maximum potential for savings
Potential for potable water savings
Electricity savings
Copyright © 2015 SciResPub.
Units
(%)
(m3/year)
(MWh/year)
Beira
76.1
6689512
2274
Chimoio
45.9
831826
1381
Tete
12.2
733223
367
Quelimane
53.2
1238402
1598
IJOART
International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
128
Although the strategies analyzed in the present study contribute to significant potable water savings for
four capital cities located in the center of Mozambique, as well as electricity savings for the water utility
company, the company will face a profit reduction due to the reduction of potable water consumption.
Therefore, the reduction of potable water consumption impacts the finances of the water utility company.
Such an impact was briefly assessed by considering only the profit reduction and the electricity savings
due to the reduction of water consumption. Table 5 presents the results for the 4 capital cities. A
maximum profit reduction of approximately MTn 165 million per year for the city of Beira, a minimum
of approximately MTn 18 million for the city of Tete and an average of MTn 58 million for each capital
city was observed. However, this might be overestimated as the local water utility company (and most
utilities in Mozambique) charges for a minimum water rate, i.e., if the water consumption of a dwelling is
lower than 10 m3 per month the water utility company charges for 10 m3. Thus, not all water savings will
impact on the water utility company profit.
On the other hand, the profit reduction that may be faced by the water utility company represents money
savings for the locals. Therefore, by reducing potable water consumption there will be not only a profit
reduction for the water utility company, but also there will be water and energy savings.
Table 5: Impact of the potable water savings on the profit of the water utility company in the center region of Mozambique
Parameter
Beira
Chimoio
Tete
Quelimane
Potential for savings (m3/year)
6689512
831826
733223
1238402
Average rate (MTn/m3)
25
Profit reduction due to the
reduction of potable water
-167237800
-20795650
-18330575
-30960050
consumption (MTn/year)
Profit due to electricity savings
2524140
1532910
407370
1773780
(MTn/year)
Balance (MTn/year)
-164713660
-19262740
-17923205
-29186270
Note: MTn stands for Mozambican Metical; on 21 February 2015 MTn 1.00 = US$ 0.03.
5. Conclusions
IJSER
The objective of this article was to estimate the potential for potable water and electricity savings by
using rainwater in the cities of Beira, Chimoio, Tete and Quelimane, located in central Mozambique.
Results of the research performed over four capital cities located in central Mozambique indicate that
potable water demand in the residential sector ranges from about 85 to 119 litres per capita per day and
there is an average rainfall ranging from about 46 to 175 mm per year. The average potential for potable
water savings is 47%, ranging from 0.44% to 164.53% on average. Such a potential is very significant,
which indicates that rainwater could be utilized for both potable and non-potable purposes. In order to
avoid the spread of diseases, rainwater for potable purposes should go through proper treatment.
For the potential for electricity savings by reducing potable water consumption, it was observed that the
highest potential was obtained for the city of Beira (2.3 GWh/year), followed by Quelimane (1.6
GWh/year), Chimoio (1.4 GWh/year) and Tete (0.4 GWh/year). The reduction of potable water
consumption means a profit reduction for the water utility company. However, this could avoid extra
costs for increasing the water pipes system. It is important to highlight that the results are based on a
theoretical analysis; therefore, in situ measurements to support the conclusions are not possible.
References
[1] Jothiprakash, V., Sathe, M. V., 2009. Evaluation of Rainwater Harvesting Methods and Structures
Using Analytical Hierarchy Process for a Large Scale Industrial Area. J. Water Resource and Protection.
1, 427-438.
Copyright © 2015 SciResPub.
IJOART
International Journal of Advancements in Research & Technology, Volume 4, Issue 2, February -2015
ISSN 2278-7763
129
[2] Ghisi, E., 2006. Potential for potable water savings by using rainwater in the residential sector of
Brazil. Building and Environment. 41, 1544-1550.
[3] Herrmann, T., Schmida, U., 1999. Rainwater utilization in Germany: efficiency, dimensioning,
hydraulic and environmental aspects. Urban Water. 1 (4): 307-16.
[4] Coombes, P. J., Argue, J. R., Kuczera, G., 1999. Figtree Place: a case study in water sensitive urban
development (WSUD). Urban Water. 1 (4): 335-43.
[5] Fewkes, A., 1999. The use of rainwater for WC flushing: the field testing of a collection system.
Building and Environment. 34 (6): 765-72.
[6] Marinoski, D. L., Ghisi, E., Gómez, L. A., 2004. Aproveitamento de água pluvial e dimensionamento
de reservatório para fins nâo potáveis: estudo de caso em um conjunto residencial localizado em
Florianópolis-SC [Rainwater harvesting and rainwater tank sizing: a case study in a multi-storey
residential building located in Florianópolis, Southern Brazil]. CLACS04-I conferência Latino-Americana
de Construção Sustentável e ENTAC04-10° Encontro Nacional de Tecnologia do Ambiente Construído,
São Paulo-SP, CD Rom. (In Portuguese)
[7] Appan, A., 2000. A dual-mode system for harnessing roofwater for non-potable uses. Urban Water. 1
(4): 317-21.
IJSER
[8] Handia, L., Tembo, J. M., Mwiindwa, C., 2003. Potential of rainwater harvesting in urban Zambia.
Physics and Chemistry of the Earth. 28 (20-27): 893-6.
[9] Li, X.-Y., Gong, J.-D., 2002. Compacted microcatchments with local earth materials for rainwater
harvesting in the semiarid region of China. Journal of Hydrology. 57 (1-4): 134-44.
[10] Worm, J., Hattum, T. V., 2006. Rainwater harvesting for domestic use. First edition, Digigrafi,
Wageningen, The Netherlands.
[11] INAM Instituto Nacional de Meteorologia [The National Meteorology Institute]. Obtained from:
www.inam.gov.mz
[12] Ghisi, E., Montibeller, A., Schmidt, R. W., 2006. Potential for potable water savings by using
rainwater: an analysis over 62 cities in southern Brazil. Building and Environment. 41 (2): 204-10.
[13] INE Instituto Nacional de Estatística de Moçambique [Mozambique’s National Statistics Institute].
Obtained from: http://www.ine.gov.mz/
[14] FIPAG Fundo de Investimento e Património de Abastecimento de Água [The Mozambican
government's Water Supply Investment and Assets Fund]. Obtained from: http://www.fipag.co.mz/
[15] EDM Electricidade
http://www.edm.co.mz/
Copyright © 2015 SciResPub.
de
Moçambique
[Mozambique
Electricity].
Obtained
from:
IJOART