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Sustainable water management in
buildings, an affordable approach. Case
Study: Terra Bio-Hotel Project, Medellín,
Colombia
Guillermo Leon Penagos García, Msc Alexander González Castaño, PhD
[Universidad Pontificia Bolivariana de Medellín [Universidad Pontificia Bolivariana de Medellín
PVG Arquitectos SAS] LEET – Laboratorio de Estudios y Experimentación Técnica
en Arquitectura]
ABSTRACT
Water management model in cities is based upon large-scale systems which take water form external
watersheds located dozens to hundred kilometers to the municipalities they supply. Water is treated to
drinking standards despite the intended use, leading to wastewater which is discharged back to the
environment through sewer systems, often without previous treatment, being an important source of
environmental pollution and public health hazards. Meanwhile rainwater is considered a problem, being
collected from roofs and streets to be also disposed in sewers as other kind of wastewater. Although water
technologies have evolved, this model has virtually remained the same since the ancient Rome, twenty
centuries ago. A paradigm shift is urgently required and buildings must be in the center of this
transformation. Terra Bio-hotel, a 41 room hotel located in Medellín is a project designed and being built
with sustainable water systems, integrating low consumption devices, rainwater harvesting, greywater
recycling and groundwater catchment. Although the building is connected to the municipal service,
altogether these strategies allow the project to function as net-zero as for water is concerned. As expected,
the water management scheme of this project is considerably more expensive than a conventional one.
Nevertheless, when operation costs are compared to conventional water fares, it appears that investment
costs are returned in five years, demonstrating eco-efficiency to be an economically sustainable choice at
this scale.
INTRODUCTION
As world urbanization increases so does the pressure upon water resources. This is particularly true
for Latin America and the Caribbean, where 80% of population lives in cities which are dependent on
external water sources to supply, where wastewater treatment is low and vulnerability to urban floods from
storm water is high (Howe, Butterworth, Smouth, Duffy, & Vairavamoorthy, 2012; World Bank, 2013)
This unsustainable condition is related to sectorial water frameworks where local governments,
environmental agencies and water companies work for contrasting agendas and measure their challenges
and achievements by divergent indicators, whereas citizens, private sector and public institutions remain
as passive users, with no say on water governance (Domenech, 2011; Bedoya, 2011)
Since urban water is mainly used and polluted through building operations; water-efficient buildings
are a reasonable starting point to give users a more meaningful role on water governance. This paper
30th INTERNATIONAL PLEA CONFERENCE16-18 December 2014, CEPT University, Ahmedabad
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describes and discusses the water management model implemented on Terra Bio-Hotel Building in
Medellin – Colombia, as a study case, whose comprehensive adoption on other building projects in Latin
America and other regions may make a significant contribution for cities to become less dependent, more
efficient, healthier, less contaminant, more resilient and more sustainable with regards to water (Howe,
Butterworth, Smouth, Duffy, & Vairavamoorthy, 2012).
OBJECTIVE
The aim of this applied research was to conceptualize, develop and implement a model for water
efficiency on a real scale building in Medellín – Colombia and to forecast the expected environmental and
financial cost-benefit ratio in order to provide governs, planners, designers and constructors a framework
to make informed decisions on sustainable water management schemes.
PROCESS APPROACH
Case study
Terra Bio-Hotel is a medium size hotel building with 41 rooms and 2400 m2 built area, looking to be
distinguished for its environmental standards at both construction and operation phases, giving host a
differential factor concerning architecture and technical facilities.The project is set in Medellín, biggest of
ten municipalities assembling a metropolitan area called the Aburrá Valley, inhabited by 3.5 million
people.
Water management data for Aburrá Valley
Information concerning water management for Aburra Valley was collected and analyzed from local
land and water plans, publications by local environmental authorities and local Water Service Company,
as well as from technical relevant literature.
Water management systems for the case of study
Prior to hydraulic design, two water system schemes were pre-designed, analyzed and compared.
System 1 is conventional, whereas System 2 is an alternative system proposed to lower the environmental
impacts related to water demand and wastewater disposal along operation phase of the building (see figure
1).
Figure 1. Water treatment systems installed at Terra Bio Hotel
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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Water treatment plants for System 2
In order to fulfill the principles for System 2, two treatment plants are required: one plant to treat
grey water to be reused on activities that do not require drinking-quality water, such as toilet flushing,
general maintenance and irrigation of green areas; the other plant is to treat rain water and groundwater
up to drinking-quality standards, to be used for showers and faucets. Both rainwater and groundwater were
previously sampled and tested for compliance to water quality regulations set for water sources intended
for domestic supply (data not shown).
Cost-benefit analysis
Financial investment costs for pre-designs of each hydraulic system scheme were calculated. Water
demand is estimated as established for hosting facilities by Colombian regulations.
Environmental costs-benefit analysis is based on the following indicators:
Total water consumption (m3/year)
Dependency on water sources external to the watershed (m3/year)
Wastewater discharge (m3/year)
Storm water discharge (m3/year)
RESULTS
Water in the local context: Water management model in the Aburrá Valley
Table 1 provides main data concerning water management in the Aburrá Valley, which is highly
dependent on external water sources despite of its high water yield. Most urban population has access to
water supply, but unaccounted for water is high. Most population also has access to basic sanitation trough
connection to a sewer network, although the level of wastewater treatment remains low. New wastewater
treatment facilities are under construction and will be fully operating by 2015 though. Due to such
investments, sanitation is charged higher than supply. Groundwater is an abundant source and it is used,
mainly by industry, but total withdraw is unknown. For building sector, such abundance becomes a
problem since parking lots and basements get below the water table, thus water has to be pumped out and
discharged into the sewer system which is charged at sanitation fares, this would also be the case for Terra
Bio Hotel project (see table 1) (Municipio de Medellín, 2014; URBAM, Área Metropolitana del Valle de
Aburrá, & Municipio de Medellín, 2011)
Table 1. Main Data Describing the Current Model for Water Management in the Aburrá Valley
Parameter Value
Water cycle balance
Valley Area (km) 1250
Average precipitation (mm/year) 1672
Average evaporation (mm/year) 1172
Water yield (mm/year) 500
Water yield (million m3/year) 625
Water supply
Total water consumption from water supply (million m3/year) 192
Dependency on external water sources –watersheds located outside Aburrá Valley-
(%) 90
Unaccounted for water (%) 40
Volume extracted from external sources, considering unaccounted for water (million
m3/year) 288
Population served (% of total urban population) 99
Wastewater
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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Combined sewer network (%) 60
Sewage currently being treated (%) 20
Water reuse 0
Population served (% of total urban population) 99
Rainwater
Rainwater use (%) 0
Conventional drainage (%) 100
Groundwater
Recharge (million m3/year) 400
Water table depth on the alluvial plain (m) 4 - 8
Groundwater extraction (million m3/year) unknown
Environmental costs comparison
Figures 2 and 3 show a water balance conceptual model for System 1 and 2
System 1 consists of:
100% of water needs supplied by the local water company
drinking-quality water is used for all purposes
no reuse is considered
rainwater is directed to sewer without use
since parking lot base is below water table, groundwater is pumped in order to prevent floods
and discharged into sewer with no prior use
Principles for System 2 are:
water needs supplied from diverse sources
water source defined according to required quality by use
reuse is considered
rainwater as well as groundwater are caught, treated and used
As shown in figures, System 1 produces more environmental impacts than System 2. Water demand
for the two systems is the same, but system 1 requires 40% more water, since it fully depends on external
sources (table 1). System 1 also produces more pollution since groundwater and rainwater are not
harvested but just discharged on sewers and grey water is not reused.
Figure 2. Water balance conceptual model for conventional water management system, System 1.
Numbers are expected volumes expressed as m3/year. Frame fill colors are related to
water quality: white = high quality, black = low quality.
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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Figure 3. Water balance conceptual model for alternative water management system, System 2. Numbers are expected volumes expressed as m3/year. Frame fill colors are related to
water quality: white = high quality, black = low quality.
Due to the use of groundwater and rain water as well as the reuse of grey water, implementation of
System 2 not just significantly reduces pollutant discharges from the project but also would eventually
allow it to be fully independent from external water sources (see figure 2), in fact, volume balances for
System 2 shows that the project may produce more water than it actually needs (see table 3)
Cost-benefit analysis
Investment cost
Table 2 lists the investments required for hydraulic installations under Systems 1 and 2 schemes.
Implementation of the efficient water management option costs as much as 38% more than implementation
of the conventional system.
Table 2. Investment cost comparison between System 1 and System 2
Item Cost for
System 1
Cost for
System 2 Description
Water pumps $ 28.947 $ 32.632
On System 2 an additional pumping system for
grey water supply is required, but the pumping
capacity required for drinking water supply gets
reduced
Storage tanks $ 10.526 $ 12.632
On System 2 an additional storage tank is required
for grey water supply, but the storage capacity for
drinking water supply tank gets reduced
Drinking water
network $ 9.944 $ 5.966
Drinking water supply network gets shorten on
System 2, since part of it is replaced by the grey
water supply network
Grey water
supply network $ - $ 6.526 It only applies for System 2
Wastewater
network $ 13.158 $ 11.053
It gets reduced on System 2 since part of it
becomes greywater supply network
Rainwater
network $ 6.642 $ 8.105
Rainwater network becomes longer on System 2 in
order to reach treatment system
Treatment
systems $ - $ 18.421 Only applies to System 2
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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Sum $ 69.217 $ 95.334
Difference $ 26.117
Operational costs
Table 3 compares both financial and environmental operation costs for the two systems, water
treatment per cubic meter under System 2 costs just 10% of the fare charged on water supply and 6% of
the fare charged on sanitation. Hence the cost of using rainwater is 10% of conventional supply.
Groundwater use and grey water reuse have a further benefit since these volumes do not get charged for
sanitation. Altogether operational cost for System 2 is 40% of operational cost for System 1, allowing full
return of the additional investment costs by year 3 of operation. On a 30 year lifecycle basis System 2
leaves the project a US $ 261000 net benefit over System 1 (see figure 4).
Table 3. Operation cost comparison between System 1 and System 2
Item Symbol Metric Value
Number of romos R 41
Water demand (m3/room/day)
According to Colombian
regulation
wd 0,5
Occupation index for hotels in
Medellín (%) oi 75%
Daily water demand (m3/day) dd r*wd*oi 15,4
Total water demand (m3/year) WD dd*365 5611,9
Total rainwater (m3/year) RW Average precipitation from table 1 *
On ground building area 534,4
Total groundwater withdraw
(m3/year) GW From case study description 3650,0
Grey water reuse (m3/year) GyW Estimated as 28% of water demand 0,0 1571,3
Dependency on water sources
external to the watershed
(m3/year)
DEW
System 1 = WD/(1-Unaccounted for
water from table 1)
System 2 = WD - GW - RW - GyW
9353,1 -143,8
Total wastewater discharge
(m3/year) WW
System 1 = WD + GW
System 2 = WD - GyW 9261,9 4040,6
Supply water costs (US $/m3) wc
Sytem 1 = supply charges from
table 1
System 2 = by treatment plant
providers
0,86 0,08
Supply anuual costs (US
$/year) SWC WD*wc 4.826 443
Sanitation charge (US $/m3) sch From table 1 1,3
Sanitation annual costs (US
$/year) SnWC
System 1 = (WD+GW)*sch
Sytem 2 = (WD-GyW)*sch 12.040 5.253
Total water system operation
costs (US $/year) WOC SWC + SnWC 16.867 5.696
Difference (11.171)
30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad
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Figure 4. Comparison of net present costs for the two systems
In spite of requiring higher investment costs, an alternative ecoefficient water management system
shows to be the best choice in order to reduce both economic and environmental costs for this case of
study. Dependency on external water sources and storm water discharge might get down to zero, as total
water demand and wastewater discharge might reduce down to 45% at a financial present net cost of 53%
as compared to a conventional water management system.
DISCUSSION
Aburrá Valley urban water management is characterized by a high dependency on external water
sources, a high unaccounted for water index, a non-regulated groundwater withdraw, a low level of
wastewater treatment and no policies on storm water discharges, leading to a vulnerable, inefficient,
pollutant system. Most Colombian and Latin-American cities might be described likewise (Howe,
Butterworth, Smouth, Duffy, & Vairavamoorthy, 2012; Domenech, 2011)
These concerns are being addressed from centralized approaches such as upgrading supply systems
and building new wastewater treatment facilities, but the role of end users is not yet being considered a
key issue. This paper shows that buildings, as end water users, would significantly improve the whole
system performance by reducing dependency, inefficiency and pollution, while significantly reducing
operational costs, leaving in fact economic benefits on a lifecycle basis (Penagos, 2007; Bedoya, 2011)
The model described here may be adopted by building projects along the Aburrá Valley, similar
approaches might be analyzed, developed and implemented in other Colombian and Latin-American
Cities, which will continue expanding in coming years under uncertain scenarios concerning incidence of
climate change on water availability, which is already a critical threat to human development in the region.
This study would be also a useful base for governments in order to promote policies and regulations
encouraging sustainable water management for healthier cities (Howe, Butterworth, Smouth, Duffy, &
Vairavamoorthy, 2012; Penagos, 2010)
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http://cus.upc.edu/publicacions/revista-sostenible/revista-sostenible-1 Domenech, L. (2011). Rethinking water management: From centralizes to decentralized water supply and
sanitation models. Documents d'Anàlisi Geogràfica, 57(2), 293-310.
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