Rainwater catchment system for disadvantaged community

Ulisses T. Bezerra1,a, Normando P. Barbosa2,b, Hector G. Morales3,c, Janean M. Shedd3,c,

Jennifer E. Hewitt3,c, Justin Fu3,c, Kelsey Evezich3,c, Matthew T. Tobin3,c, Uzoma B.

Ayogu3,c, Wanyi Ng3,c, Diego S. Amorim2,d, Guilherme O. Oliveira2,d, Helen K. R. F.

Pinto2,d, Jacqueline G. Silva2,d, Jessé P. Gomes Júnior2,d, Márcio S. Gonçalves2,d, Rafaela

L. Silva2,d, Roberto M. P. F. Mendonça2,d

1Federal Institute of Paraiba-IFPB, Av. 1º de Maio, 720, Jaguaribe, João Pessoa-PB,

Brazil, 58015-435

2Federal University of Paraiba-UFPB, Center of Technology – LABEME, Campus I, Cidade

Universitária, s/n, Castelo Branco, João Pessoa-PB, Brazil, 58051-900

3DUKE University, Pratt School of Engineering, 100 Science Dr, Durham, NC 27705,

United States of America

adartarios@yahoo.com.br, bnperazzob@yahoo.com.br, cjennifer.hewitt@duke.edu,

dhelenkrfp@gmail.com

Keywords: water sustainability, rainwater tank, toilet flushing, disadvantaged community. Abstract. A partnership between Federal University of Paraiba - UFPB (Brazil) and DUKE

University (USA) chose an economically-impaired community in Northeastern Brazil for the

implementation of a rainwater catchment system. The goal was to collect rainwater for using it in

toilet flushing in order to achieve: (i) water consumption reduction; (ii) use of gravity force; (iii)

electric consumption reduction; (iv) utilization of an extra water source. This project, started in the

end of 2013, was developed during the first semester of 2014, and implemented from July to

August, 2014. For this purpose, engineering undergraduate students from DUKE University

traveled to Brazil and, joining the Brazilian academic group. They constructed two rainwater

catchment systems as well as the supply piping for three bathrooms. Each system was built in a

different location: one in a place belonging to a non-governmental organization and the other in a

local popular home. Low-cost construction materials were employed, always aiming to follow

safety and sanitary normative requirements. The tanks are located in an intermediate height between

the roofs and the toilet water inlet so that the water is conducted along the piping by gravity only.

Results have shown that: (i) water consumption decreased in both systems, (ii) rainwater is

currently used with efficiency, and (iii) electric consumption was also reduced. Henceforward, the

main idea is to propose to local governments the adoption of such rainwater catchment systems for

all the community (500 families) as to introduce a sustainable use of water from rainfalls.

Introduction

Despite the economic development that has occurred in emerging countries during the last

decades, a certain portion of society remains on the margins of social and economic progress. In

these countries, peripheries of big cities present many infrastructure problems. In addition, the lack

of adequate housing conditions, water, sanitation, etc., are part of a disturbing reality, where the

most affected are those who are more vulnerable: the children and the elderly [1]. In Brazil,

hundreds of low-income communities suffer from problems related to the insufficiency (or even

absence) of essential elements of urban infrastructure.

In terms of statistical data, according to the Brazilian Basic Sanitation Plan (PNSB) [2], less than

60% of the national population has access to collection and treatment sewage systems, which are

basic services to be provided for citizens.

Given this scenario, the Brazilian government has established development policies related to

university extension programs that support projects aiming to approach the society and academia.

This new paradigm in higher education has attracted specific actions towards the application of

theoretical knowledge to solve both recurring and urgent everyday problems faced by citizens.

In this context, the present community work project of the Federal University of Paraiba (UFPB)

aimed at dialogic interventions in the scope of the housing infrastructure, in a partnership with the

organization DUKE Engineers for International Development (DEID) [3], from DUKE University

(Durham, US), and the Non-Governmental Organization (NGO) Casa dos Sonhos [4] (Santa Rita,

Brazil).

The interventional actions were planned at UFPB’s Center of Technology, with tasks divided

into groups of students and professors from the respective universities. All the phases of the project

(description of constructive methods, sizing of pipes, definition of construction materials, etc.), as

well as further actions, were done during the initial project steps in the respective institutions. Later,

the execution activities were carried out with the presence of DUKE students in Brazil.

Thus, the goal of this project was to conceive and implement a rainwater catchment system that

allows the use of rainwater in toilet flushing in houses of the community, through a bilateral work

of two higher education institutions (UFPB and DUKE).

Materials and methods

The project was performed during eight months and was composed of three phases.

In the first phase, UFPB engineering students realized some visits to the community for

recognition of its socioeconomic reality and diagnosis of its main infrastructure problems related to

the proposed project.

Secondly, the intervention actions to be developed in the community were formulated,

prioritizing cost reduction. Then, weekly meetings were set for project conception. The DUKE

team’s task was to design the rainwater tanks as well as to choose and estimate the materials needed

for their construction, whereas the UFPB team was responsible for the design of the necessary

piping for the rainwater catchment - and toilet flushing - system.

During the first two phases, a constant communication was established between UFPB, DUKE

students, the project coordinators (professors from both universities), the NGO and the community,

in order to assure that every action was compatible with the needs of the beneficiaries of the project.

In the third and last phase, the students (from UFPB and DUKE), UFPB professors, NGO

members, and other volunteers implemented the developed designs during over one month in the

community. UFPB gave support to the students by offering a van to transport the students from and

to the community on a daily basis. The project was brought to public attention through television

and online social networks.

Two places were chosen for the rainwater catchment systems, where the tanks would be built:

one tank at the NGO Therapy Center (with four roofs) and one tank at the house of a community

resident. The catchment system is composed of the gutters that collect the rainwater from the roofs,

a diverting system that will discard a first portion of the rainwater, piping that takes the water

into/from the tank, water tanks and other accessories.

The Brazilian Standard for the use of rainwater for non-potable purposes, NBR 15527 [5], states

that a certain volume of rainwater has to be discarded by flush diverters, due to the presence of tree

leaves, small debris and organic matter from the roofs; such volume depends on the roof area from

which the water is collected and prevents the system from having flow impairments or a bad water

quality. For this purpose, barrels were installed to the piping, before the connection with the tanks,

in order to catch and discard the first volumes of water. Once these barrels are filled up with the

dirtier water, they are automatically closed and the cleaner water continues to be driven to the tanks.

Finally, once the rainwater is stored, it is directed to toilet flushing and can be used in the

bathrooms of four houses.

Figure 1. NGO floor plan with the piping system detached. Gutters (magenta color) conduct

rainwater from roofs to pipes (yellow color). The inlet piping (also in yellow) connects the reservoir

(blue rectangle). Outlet piping is shown in green color, leading the stored water from the tank to

toilets (red circles).

Rainwater flow estimate

First the volume of water to be collected per hour of rain on the roof was estimated. According to

the Brazilian standard NBR 10844 [6], which regulates rainwater catchment systems in buildings,

the rainfall intensity (i.e. the thickness of a water layer over a 1m² area) to be considered depends

on the location of the construction site. A rainfall return period of five years and a duration of five

minutes were considered for choosing the adequate rainfall intensity.

Because no statistical data was found for the city of Santa Rita, the rainfall intensity was adopted

to be the same as that of Joao Pessoa, approximated to 140 mm/h in the standard table, which is the

capital of the state. This consideration can also be justified by the fact that Joao Pessoa is the

nearest big city and its metropolitan region comprises Santa Rita. Then, no significant differences

would be found between these urban centers, in terms of data related to rainfall features, as both are

subject to similar meteorological phenomena.

Sizing of gutters and piping system

The flow rate of water to be collected by gutters of a roofing, which is called design flow rate, is

a function of rainfall intensity (I, in mm/h) and the area of contribution (A, in m²).

(1)

Design flow rate equation

Q: design flow rate (l/min)

I: rainfall intensity (mm/h)

A: area of contribution (m²)

The gutters and piping until the tanks are designed as free conducts through Manning’s equation

and should have a uniform slope of at least 0.5% and up to 1.0%. Thereafter, the dimension

estimate of the vertical and horizontal pipes was found out through abacuses and tables presented in

the NBR 10844 standard.

(2)

Manning’s equation

Q: design flow rate (l/min)

S: cross-sectional area of flow (m²)

: hydraulic radius (m)

I: rainfall intensity (mm/h)

n: Manning’s coefficient

Rainwater tanks

Many construction materials were considered for use on the tanks. For each construction site,

different solutions were adopted, prioritizing the economic sustainability of the applied building

methods and taking into consideration spatial restrictions. At the NGO Therapy Center,

conventional masonry blocks (containing eight holes) were used to build the walls to support

prefabricated concrete slabs. At the house, pre-fabricated containers were utilized with a supporting

foundation built in conventional masonry bricks as well. Each tank contains a piping system that

not only has its inlet and outlet pipes, but also two others that allow for the tank’s overflow (on the

top) and complete drainage (on the bottom), if necessary.

Toilet flushing system

The piping needed to direct the water stored in the tanks towards the bathrooms was designed as

pressurized cold water conducts, according to the Brazilian standard NBR 5626/1998 [7], which

regulates water supply systems in buildings. The design aimed at using gravity force only to drive

the stored rainwater with satisfying pressure levels that would enable toilet flushing. This pressure

level at the connection point to the toilets should be 0.5 meters of water column.

Results and discussion

For a better understanding of the results achieved on the performance of the tanks, the rainwater

catchment systems are henceforward distinguished from each other: the System #1 corresponds to

the system implemented at the NGO Therapy Center and the System #2 refers to the one built at a

house of the community.

a) System #1 (NGO)

Gutters

At the construction site, some preexisting gutters already collected rainwater from part of the

roofs. These gutters were made of PVC (PolyVinyl Chloride) pipes with 150 mm of diameter, cut

longitudinally in half, or made of metallic plates in a rectangular transversal profile. All gutters

were cleaned for reuse and some had their direction of slope inverted, according to the project

requirements. Other gutters were installed in roofs where no collecting systems were found.

The slope required for the gutters was 0.5% [6] and it was reached by using a level tube (Figure

2).

Figure 2. Adjustments of gutters after establishing the project slope.

Tank’s foundation

It was discussed with the NGO members the most feasible spot for the construction of the tank.

Once it was defined, foundation ditches measuring 10 cm in depth and 40 cm wide were dug. A

lean concrete layer was cast in the ditches. Concrete specimens (Figure 3), obtained from the

technological control of other constructions, were used replacing stones. Then, foundation walls

were built (Figure 4). Over them, concrete channel blocks (30 cm x 19 cm x 15 cm) were placed.

Two parallel 10 mm steel bars were put into the channel blocks. After that, a concrete mixture (4

parts sand, 4 parts coarse aggregate, 1 part cement, by volume) was cast into the channel blocks,

covering the reinforcement bars.

Figure 3. Concrete specimens used as foundation elements.

The level of the bottom slab of the tank was fixed according to the design water pressure

required to the toilets, considering hydraulic losses in all pipe sections. The tank could not be built

on the ground level because the water would not reach toilet flushing with enough pressure without

the use of electricity. According to the NBR 5626/1998, the minimum necessary hydraulic pressure

for servicing toilets is 0.5 meters of water column.

One end of the level tube was placed at the highest inlet pipe among the project’s flushing

cisterns and the other end was placed at the level of the tanks foundation. Then, bricks were laid

until the latter level (foundation level). A line was used for marking levels and rows of bricks were

built until it reached 30 cm below the foundation level. For every row of bricks constructed,

horizontality was assured.

The last layer in the wall over the foundation consisted of another tie beam made of channel

blocks (similar to those previously used). The height of this layer was 15 cm. The additional 15 cm

corresponded to the distance between the lower inner surface and level of the outlet piping in order

to allow the sedimentation of debris in this non-utilized volume of water (Figures 4 and 5) and to

avoid having a dirty water go to the toilets.

Figure 4. Scheme of the NGO reservoir. Figure 5. Construction of the second tie beam.

Slab tank

A bottom precast slab was built over the foundation walls. Small prefabricated reinforced

concrete beams were arranged over the foundations’s last layer of channel blocks. In the transversal

direction. Ceramic bricks were placed between the concrete beams (Figure 6).

A steel mesh was placed over the blocks and tied to the beams. After setting up a wooden form,

concrete mixture was released on the structure.

Figure 6. Slab structure in the base of the tank.

Masonry

Firstly, reinforced concrete pillars were built. Next, more rows of bricks were added. At the level

of 40 cm, measured from the base of the tank, a third tie beam was constructed (with the same

procedure used for the previous ones) as to assure the stiffness of the masonry walls. The thickness

of this beam is 12.5 cm, being narrower than the first two tie beams. Four more row bricks were

added over this beam and a final tie beam was built near the top of the tank (Figure 7). Another slab

was built on top of the walls as the tank’s ceiling.

Figure 7. Position of the beams at the base and at the half height of the tank.

Inlet piping

Design indicated a 100 mm diameter for the inlet PVC pipes. A small mesh net was installed at

the entrance of the piping system to avoid obstructions caused by debris. The PVC tubes were fixed

onto the walls of the property by steel clamps. The clamps were screwed to the walls every 3 meters

keeping the design slope. All pipe connections were sealed with appropriate silicon sealant.

In total, two inlet tubes were installed on the tank: one collects rainwater from a roof that

belongs to the NGO, whereas the other pipe catches rainwater from other three nearby houses of the

community. Each of the inlet tubes has its own flush diverter.

Because there is a difference between the levels at which each inlet pipe intersects the tank, i.e.

the pipe from the NGO roof is 30 cm higher than the other inlet pipe, a check valve was installed in

the lower tube. It prevents water reflux in the lower tube, when the water is near the maximum level

inside the tank. When this happens, the rainwater flow in the lower inlet pipe no longer contributes

to fill the tank and may be discarded through its flush diverter.

Outlet piping

There are two pipes for the outlet flow: one tube is connected to the NGO toilet and the other

conducts the water to three other toilets (community houses). The diameters of both pipes are 45

mm and 50 mm, respectively. The outlet pipes are placed at 15 cm and 23 cm, respectively, from

the level of the lower slab (Figure 8).

Figure 8. Outlet pipe with hydraulic valve.

All outlet pipes run below the ground level. For the NGO toilet, a small ditch was dug (10 cm

deep) from the tank to the toilet. A PVC pipe, with 45 mm of diameter, was then placed into the

ditch. At the toilet wall, a hydraulic component was applied to reduce the diameter from 45 to 20

mm)

Simultaneously, PVC pipes (diameter of 50 mm) were installed towards the other houses. A tee

connection was utilized to derive water from the House #2 to House #3. The end of the pipe that

feeds the House #2 is submitted to a reduction from 50 mm to 20 mm. In the House #3, the inlet

pipe is connected to the toilet tank. Another valve was installed in the preexisting piping system, as

to permit the use of either city water or tank water. A similar scheme was adopted for House #2.

b) System #2 (community house)

Tanks

Due to time constraints and aiming at the adoption of a rationally economic method, it was

decided to acquire three small containers with a 1 000 liters volume, each one, that were installed

side by side over a concrete slab. Each tube contains a central lid at the top. There is also a tap at the

base of each reservoir for complete drainage.

Foundation

The second catchment system was built at the backyard of a community house. The foundation

of the tanks was performed through a constructive process similar to the foundation executed at the

NGO tank (Figure 2). Ditches (35 cm wide, 20 cm deep) were dug for supporting the tank

foundation. The dimensions adopted for the foundation were 1 meter high, 1 meter wide and 3.3 m

long (Figure 9).

The ditches were filled out with concrete specimens and mortar until the ground level. The first

row of bricks (19 cm x 19 cm x 10 cm) was then placed. Differently from the foundation of the first

tank, channel blocks were not used at this stage. A layer of 1.5 cm of mortar was done.

Figure 9. Foundation of the tanks of System #2.

Slab

The precast slab structure was built over the masonry layers of bricks. Reinforced concrete

beams were placed in the horizontal plane. Thus, after putting ceramic blocks between concrete

beams, the concrete mixture was cast over this structure. The slab is 15 cm high (Figure 10).

Figure 10. Construction of the slab.

Gutters and piping

The house that started being supplied by the tanks already had a gutter that catches rainwater

from half of its roof. Instead of capturing water from the other half of the roof, the project members

decided to capture rainwater from a neighboring church’s roof, which was much larger, with proper

permissions. As a result, time and financial resources were saved.

The preexisting gutter had a diameter of 150 mm (PVC pipe longitudinally cut in half).

Screwed metallic clamps were used to attach the gutter to wood elements of the roofing frame.

The slope of the gutter was changed (to 0.5%) as to conduct the water towards the house backyard.

The same sealant procedure, as taken in System #1, was carried out for System #2

It was used an inlet pipe for the tanks, made of PVC, with 100 mm of diameter. A diameter

reduction (150 mm to 100 mm) device was also implemented between the gutters and such pipe. It

was also installed a little mesh to retain any debris from the roofs. Tee connections were also

utilized in these installations (Figure 11b). The flush diverters, for discharging of the first rainwater

volumes, have 100 liters of capacity with a drain outlet located at the base of this container.

A silicon-based sealant was applied at the connection between the inlet pipe and the entrance of

the tank.

Figure 11. Pipes that connect the three tanks (a) and the inlet piping (b).

The outlet piping catches rainwater from the three tanks and conducts it below the ground level

towards the house toilet. A closure valve was installed in this section (Figure 12).

(b) (a)

Figure 12. Outlet piping (brownish pipe)

Difficulties encountered in the project

Project and execution

Prior to the teams’ arrival in Brazil, the previous plan considered the construction of cylindrical

tanks. It was thought that this geometric form would lead to utmost cost-effective relation, in terms

of the amount of necessary construction material to be used and the water volume to be stored.

However, after inspections on the construction site, it became evident that rectangular tanks would

be more efficient in both spots (NGO property and house), due to the avoidance of structural

problems, higher speed of construction and optimized usage of the available area for construction.

For the next versions of the project, more planning will be dedicated to the optimum location of

tanks as a function of the height of the tubes coming from the gutters (System #1). Although an

innovative solution was performed for dealing with the difference of levels between inlet pipes, it

required more time of construction. The ideal solution would be establishing the same level for both

pipes. On the other hand, the tanks were built in the best possible locations, according to the

circumstances encountered.

The Project members would have preferred to build a tank for the house (System #2).

Nevertheless, because of time and space constraints, three premade containers (composed of a

polymeric material) were bought. These containers had smaller water capacity (1000 liters each)

and were of difficult maintenance

Communication and logistics

At the beginning of the project, there was some difficulty in communication among project

members, due to different language backgrounds (Portuguese and English). It interfered in

performing tasks at the site. Sometimes, services were made incorrectly and it needed more time for

correction. Over the days, communication between project members and people from the

community improved, becoming faster and more precise.

The Federal University of Paraiba provided logistic support for the transportation of project

members towards the construction site. However, this project also suffered from setbacks related to

transport of students and materials to the construction site, which has to be improved for future

related projects. Delays in the supply of materials, e.g. cement, bricks, pipes, etc., made it difficult

to meet some project deadlines.

Conclusions

The intervention actions developed at the community took place as projects in the engineering

field, having the engagement of several people from various undergraduate courses at UFPB,

DUKE and even other universities. This experience also involved the participants with activities

related to different academic areas of knowledge, which contributed to raising global and local

awareness and to the training of people.

Through the close contact with the community and the assistance of the NGO staff, students

could establish a diagnosis of the infrastructure as well as social and economic aspects of the

community and propose solutions to real problems based in social, environmental and economically

sustainable measures.

Therefore, the partnership with DUKE University and UFPB managed to develop a double

interaction: (i) integration of knowledge acquired by students and professors from both universities

and (ii) physical integration (through interpersonal relations) between the community and the

universities.

Finally, the project was reported by a local television station, social media and UFPB and DUKE

Websites as tools for broadcasting such extension experience.

Future trends

The partnership between both UFPB and DUKE universities intends to continue, as a mutual

work for development of future extension projects that may cover further areas of knowledge. Thus,

the goal is to give subsidies to achieve significant changes the infrastructure of this community and,

consequently, to bring better quality of life for the people and also opportunities for social

development for locals.

In terms of project plans, it has been planned to build other constructions with Mattone blocks

(soil-cement bricks), due to the ecological viability they present and also aiming at providing

adequate living conditions for citizens. Furthermore, it has also been planned to implement the

rainwater catchment system, for non-potable usage, in future construction works, for executing

models of sustainable construction. Other constructions, such as houses can also be donated to local

needy families.

Additionally, there is a possibility to construct a public library that will belong to the NGO,

covering a target audience and contributing to the improvement of the education system proposed

and offered by the NGO Casa dos Sonhos.

Acknowledgments

We are grateful to Helen Karla Ramalho de Farias Pinto, DUKE University and the group Duke

Engineers for International Development (DEID), Prof. Margareth Diniz, Rector of UFPB, that

collaborate with some financial support, Prof. Gilson Barbosa Athayde Júnior, from the Federal

University of Paraiba, Casa dos Sonhos NGO, UFPB engineering students as well as all volunteers

engaged in this project.

References

[1] BRUNDTLAND, Gro Harlem. Our common future: world commission on environment and

development. Second edition. Rio de Janeiro: Getúlio Vargas Foundation. 1991.

[2] Secretariat for Strategic Affairs (SAE). Published approval of the National Sanitation Plan

(PNSB) in the Official Gazette on Friday. Source:

http://www.sae.gov.br/site/?p=19554#ixzz3CyCDgxCs.

[3] Duke Engineers for International Development. Available at http://sites.duke.edu/deid/.

[4] Social Statute of the Non-Governmental Organization ‘Casa dos Sonhos’. 2009. Available at:

http://www.casadosonhos.org/Estatuto%20social.php

[5] Brazilian National Standards Organization. NBR 15527: Rainwater – Catchment of roofs in

urban for non-potable purposes - Requirements. 2007.

[6] Brazilian National Standards Organization. NBR 10844: Building facilities for rainwater. 1989.

[7] Brazilian National Standards Organization. NBR 5626. Cold water building installation. 1998.