FEASIBILITY AND REVENUE OF RAIN WATER HARVESTING SYSTEMS (RWHS) IN DAVAO A N ANALYSIS USING SIMULATION
Simulating revenue of RWHS for different variables over 23 years of rainfall data, combined with literature to study feasibility and most effective implementation. Part of Bachelor Built Environment Third year internship research water management at Rotterdam University of Applied Science. Project Document name Version Organizations Website Author Date, Location
Feasibility of Rain Water Harvesting Systems B.01 4.2 HELP Davao, TropICS, Ateneo de Davao, DOST XI http://davao.vincentoskam.nl Vincent Oskam 21 December 2012, Davao, Philippines
Region XI Davao
Feasibility and revenue of Rain Water Harvesting Systems (RWHS) in Davao An analysis using simulation
II. METHODS I. INTRODUCTION Davao City is one of the largest cities in the world based on land surface. The tropical climate in the southern Philippine island Mindanao receives more than 1000 mm of rain per year. The short duration intense rainfall leads to overload of the drainage systems, while wasting the valuable free source of (rain)water. Without treatment, rainwater can be used for non-health purposes like CR flushing. This study uses simulation to assess the effectiveness and feasibility of Rain Water Harvesting System (RWHS) implementation in the Davao City area.
KEY FINDINGS RWHS revenue is greatly dependent on the factors and variables catchment area, usage and tank size. The rainfall can only be stored up to the maximum tank capacity, revenue is limited by the effective usage of the RWHS. These variables lead to far lower revenue than expected with popular formulas. They also reduce the mitigation effect on drainage load significantly. Maximum retention capacity is the tank size divided by the catchment area. For a 1000 m2 surface with 2 m3 tank it is maximum 2 mm for that 1000 m2. Tanks are high investments and the RWHS is expected to have long Return Of Investment (ROI) time and relatively low revenue.
LITERATURE As basis for this feasibility study, literature on RWHS is consulted defining the different strategies, design criteria and best practices. As primary basis the (Texas water development board, 2005) publication is used. All cited works are referred to using APA 6 in chapter Works cited at the end of this pulication.
SIMULATION To calculate revenue RWHS of different tank sizes and daily usage are simulated over 23 years of rainfall data from Pag-Asa Davao: 07˚ 07’N, 173˚ 39’E 18m +MSL. For the years: 1985-1986, 1989-1995 and 1997-2010. Simulation is done using Microsoft Excel 2010 © with the following formulas. → → → → ̃
∑ ∑
̃ ∑
ORGANIZATION OF THE PAPER Chapter II explains the methods used for simulation, chapter 1. Covers the basics of RWHS and chapter 2. Shows the simulation results. Finally chapter 3. contain conclusions.
Vincent Oskam, 2012
To ensure replicability and reliability of this research, the used methods are described below.
Storage in reservoir on day n Storage in reservoir on day n-1 (the day before) Volume of the reservoir Precipitation on day n Usage on day n Revenue on day n Average daily revenue Total of days n
When daily usage is higher than available in the storage tank, the maximum available is assumed.
http://davao.vincentoskam.nl
D.ID B.01…. 2 of 10
Feasibility and revenue of Rain Water Harvesting Systems (RWHS) in Davao An analysis using simulation
1. BASICS, POLICY AND
PRACTICE The source of water is the rainfall on the catchment area, that can effectively be collected in the storage. Rainfall minus evaporation, splash-out, inverted run-off, etc. The area that is used to catch the rainwater is called the catchment area. The catchment area will need sufficient slope and facilities to discharge the water to the storage. The storage is used as buffer for the non-rainfall events. The advantage of elevated storage is that it can be used without the help of an extra pump. Note that storage of large Vincent Oskam, 2012 Illustration 1.1
amounts of water result in high weight on buildings, construction stability and safety should be taken into consideration. Collected rainwater can be used untreated for non-quality demanding purposes, like toilet flushing or gardening. It is not to be used for drinking, dishes etc without proper threatment. To use the collected rainwater as drinking water or other quality demanding purposes, it should be properly filtered and treated to ensure safety and health. 1
1
Consult expert before using for health purposes.
http://davao.vincentoskam.nl
D.ID B.01‌. 3 of 10
Feasibility and revenue of Rain Water Harvesting Systems (RWHS) in Davao An analysis using simulation If gravitational flow of the collected water into the building is not necessary, undesirable or impossible, a storage tank on ground level or underground can be used. The water can be used for gardening under gravitational flow or as slow storm water discharge or aquifer recharge area. To use water from storage on ground level, a pump can be used for water transport into the building. The pump will have to be strong enough to overcome resistance in the pipes and gravitational force to the highest connection in the building. That is why preferably elevated storage is used to use the gravitational flow of water. Ground level storage can be used without a pump for gardening, for example in dry periods. The harvested rainwater can also be stored with the sole purpose of temporarily retaining storm water, prevent soil erosion and/or aquifer recharge.
RWHS IN POLICY RWHS is covered or connected by national laws, ordinances and guidelines.
NATIONAL LAW In March 17 of 1989 Republic act 6716 was approved, inter alia stating that “The Department of Public Works and Highways (DPWH) shall … undertake construction of water wells, rainwater collectors, development of… …every barangay in the country shall have at least one additional potable water source. …”. (Republic Act No. 6716, 1989)
LOCAL LAW Davao City Rainwater Ordinance of 2009 states inter alia that “All construction of new commercial and industrial buildings including Vincent Oskam, 2012
major renovations … public and private buildings must include an RCS. … RCS must be integrated in existing government buildings, specially public school and public markets. …”.2,3 (Rainwater ordinance 0298-09, 2009)
INTERNATIONAL GUIDELINE World Health Organizations publication: Guidelines for Drinking-water Quality third edition inter alia covers local government’s responsibility on drinking-water supply and water quality: “… Local health authorities play an important role in managing water resources and drinking-water supplies. … Local authorities will also give specific guidance to communities or individuals in designing and implementing community and household drinking-water systems and correcting deficiencies… Management of household and small community drinking-water supplies generally requires education programmes about drinking-water supply and water quality … include: Water hygiene awareness, basic technical training…, …, a system of continued support, follow-up and dissemination of the water quality programme to achieve and maintain sustainability.” (World Health Organization (WHO), 2008)
NATIONAL GUIDELINES Administrative order No. 2007-0012 from the Department of health states inter alia: “… Local Health Authority at the municipal or city level shall identify the list of paramters that will be examined to determine the potability of drinking water … undertake a systematic assessment of all the parameters listed in the 2007 Philippine National Standars for Drinking Water (PNSDW 2007)… ”. (Department of Health, 2007) RCS: Rainwater Catchment System Status and reviews of the ordinance must be checked before basing conclusions on this citation. 2 3
http://davao.vincentoskam.nl
D.ID B.01…. 4 of 10
Feasibility and revenue of Rain Water Harvesting Systems (RWHS) in Davao An analysis using simulation
2. REVENUE SIMULATION DEFINING FACTORS Revenue, TCO and ROI is dependent on several proportional and inversely proportional factors.
CATCHMENT AREA SIZE The rain water harvesting potential is proportional dependent on the catchment area size. For every square meter the potential is calculated in liters as 1 * [rainfall in millimeter].
PRICE OF WATER
5 mm 10 mm 20 mm 40 mm 60 mm 80 mm
To calculate financial revenue, Total Cost of Ownership (TCO) and Return Of Investement (ROI) the reduction in water bill is calculated assuming a reduction in tap water usage equal to the RWHS revenue. Price of water in Davao City is dependent on the monthly usage, increasing with higher usage. 11-20 3 m 14.40
21-30 3 m 18.60
31-40 3 m 24.70
41-50 3 m 36.00
51-up 3 m 36.00
Table 1 Price of tap water in Davao City in PHP 2013 (WDInfo, 2011)
500 m2
1000 m2
0.5 m3 1 m3 2 m3 4 m3 6 m3 8 m3
2.5 m3 5 m3 10 m3 20 m3 30 m3 40 m3
5 m3 10 m3 20 m3 40 m3 60 m3 80 m3
Table 3 Indication of RWHS potential
STORAGE TANK SIZE The maximum potential rain water harvesting is limited by the size of the storage tank. After the tank is filled, precipitation can no longer be stored and will flow over via relief valves to the storm water drainage system.
DAILY USAGE
COST OF IMPLEMENTATION Initial investment in material en services. Material Water tank 1m3 Water tank 1.5m3 Water tank 2m3 Assumed 2 days of plumbing services Assumed various plumbing materials Cost of yearly maintenance
100 m2
Cost 21 125.00 PHP 26 125.00 PHP 32 000.00 PHP 700.00 PHP 3000.00 PHP 30 minutes per week or 26 hours per year
As rain water, untreated, cannot be used as replacement of potable water, revenue is limited to the non-health usage purposes of harvested rain water. For example flushing toilet flushing and gardening. An American StandardŠ toilet generally has a 6.06 liter (1.6 gallon) tank. Allowing for 165 flushes per square meter rain water harvesting. Or assuming 2 toilet visits per office day per FTE 4 , 82 FTE can be accommodated.
Table 2 Indication of investment cost (ICE Hardware shop, 2012)
4
Vincent Oskam, 2012
FTE Full Time Employee
http://davao.vincentoskam.nl
D.ID B.01‌. 5 of 10
Feasibility and revenue of Rain Water Harvesting Systems (RWHS) in Davao An analysis using simulation
SIMULATING REVENUE Using the simulation process described in chapter Methods, the complex relationship between the variables is shown. It is not possible to devise a simple formula to calculate the revenue.
CATCHMENT AREA The rain water available in the storage tank is dependent on the catchment area, larger catchment areas require less rainfall to fill the tank, increasing rainwater availability. Illustration 2.2
TANK SIZE The tank is used to store water for the days without or little rain. The larger the tank, the more dry days it can buffer. When average daily usage is low, the increase in revenue slows down for larger tanks.
Illustration 2.1
USAGE Harvested rainwater without treatment can only be used for non-health purposes. Therefor the revenue is limited by the daily usage. Revenue is equal to the amount of harvested rainwater actually being used. Revenue increases with daily usage, until usage is equal to tank size.
Illustration 2.3
Illustration 2.4 on the following page shows an overview of several different factors and variables.
Vincent Oskam, 2012
http://davao.vincentoskam.nl
D.ID B.01‌. 6 of 10
Feasibility and revenue of Rain Water Harvesting Systems (RWHS) in Davao An analysis using simulation
Daily revenue in cubic meters
0.6 0.5 0.4 0.3 0.5 M^3 0.2
1 M^3
0.1
1.5 M^3 2 M^3
0 S50 U120
S50 U240
S200 U240
S200 U500
S500 U500
S500 U1000
S1000 U1000
S1000 U2000
(S)urface area in square meters (U)sage in cubic meters a day
Illustration 2.4
FINANCIAL REVENUE Financial revenue is proportional to the price of water per cubic meter.
Illustration 2.5
Vincent Oskam, 2012
RETURN OF INVESTMENT (ROI) ROI depends on daily revenue and implementation cost. Implementation cost increases with tank size.
Illustration 2.6
http://davao.vincentoskam.nl
D.ID B.01‌. 7 of 10
Feasibility and revenue of Rain Water Harvesting Systems (RWHS) in Davao An analysis using simulation
3. CONCLUSIONS Rain Water Harvesting System (RWHS) implementation is mandated by national law and local ordinance. Due to high implementation cost, maintenance and low revenue, filtering rain water to health purpose water is not advised. However, should rain water be used for health purposes national Department of Health and World Health Organization guidelines states the local government is responsible for guidelines assuring quality. RWHS revenue calculated by advised formulas, using average rainfall, overestimate the actual revenue simulated over rainfall data in Davao. The complex relation between catchment area, tank size and maximum nonhealth usage potential, result in lower actual revenue.
On general it can be said that larger tank sizes are advised for buildings with catchment areas greater than 500 m2 and maximum potential usage of 500 liters per day. On the whole, RWHS is not very revenues for smaller catchment areas. When implemented on small catchment areas, larger tank sizes will result in relative low increases in revenue while implementation cost almost doubles between a 1 m3 and 2 m3 tank. It must also be noted that RWHS will only result in mitigation of the storm water drainage until the tank is filled. High intensity rainfall events will quickly fill the RWHS tanks, actual mitigation during high intensity rainfall is therefor expected to be low as long as tank sizes remain small.
The size of the tank defines the amount of water that can be stored in dry or little rainfall days, larger tanks result in higher revenue. Larger catchment areas need less rainfall to fill the tank, thus also resulting in higher revenue. The revenue is equal to the amount rain water actually being used for non-health purposes, higher usage potential, i.g. the number of toilet flushes a day. The relation between variables is to complex to be calculated with a simple formula. For actual revenue calculations and best implementation practices a custom simulation is advised. The simulation program used in this paper is available on http://davao.vincentoskam.nl . It must be noted that simulation over the Pag-asa Davao rain gauge does not necessarily provide an accurate prediction for all locations in Davao and not at all for areas outside of Davao.
Vincent Oskam, 2012
http://davao.vincentoskam.nl
D.ID B.01‌. 8 of 10
Feasibility and revenue of Rain Water Harvesting Systems (RWHS) in Davao An analysis using simulation
III.
Works cited
Ruelo, R. (2012, November). Water usage and maintenance DOST. (V. Oskam, Interviewer) Republic Act No. 6716. (1989, 5 17). AN ACT PROVIDING FOR THE CONSTRUCTION OF WATER WELLS, RAINWATER COLLECTORS, DEVELOPMENT OF SPRINGS AND REHABILITATION OF EXISTING WATER WELLS IN ALL BARANGAYS IN THE PHILIPPINES. Philippines. Retrieved 12 24, 2012, from http://www.gov.ph/1989/03/17/rep ublic-act-no-6716/ Rainwater ordinance 0298-09. (2009). Davao City Rainwater Ordinance of 2009. Davao City, Philippines: City Council. Ateneo De Davao University. (n.d.). Central_911. Retrieved 11 3, 2012, from WMDAS: http://202.91.163.247/wmdas/ws Bacongco, K. (2012, 01 26). Davao water distrcit justifies price hike. Retrieved 10 12, 2012, from philSTAR.com Mindanao: http://www.philstar.com/nation/arti cle.aspx?publicationsubcategoryid=20 0&articleid=771462 CSG Network. (n.d.). Water Consumption Calculator. Retrieved 5 11, 2012, from CSGNetwork.com: http://www.csgnetwork.com/wateru sagecalc.html Davao City Water District. (2010-2011). Water bill. DCWD. de Amado, J. (2007, 05 19). The rainwater havesting system. Inquirer lifestyle. Retrieved 10 30, 2012, from http://showbizandstyle.inquirer.net/l ifestyle/lifestyle/view/20070519-
Vincent Oskam, 2012
66830/The_rainwater_harvesting_sys tem de Amado, J. (2007, 05 19). The rainwater havesting system. Inquirer lifestyle. Retrieved 10 30, 2012, from http://showbizandstyle.inquirer.net/l ifestyle/lifestyle/view/2007051966830/The_rainwater_harvesting_sys tem de Vera, E. B. (2012, 03 25). DENR urges adoption of rainwater harvesting. Manila Bulletin, p. 1. Retrieved 10 30, 2012, from http://www.mb.com.ph/articles/249 501/denr-urges-adoption-rainwaterharvesting#.UI8ntcVLP5M DENR. (1994). DENR Administrative order NO. 26-A. Department of Health. (2007). Administrative order No. 2007-0012 . Philippine National Standards for Drinking Water 2007. Philippines. Retrieved 12 24, 2012, from http://www.lwua.gov.ph/downloads_ 10/Philippine%20National%20Stand ards%20for%20Drinking%20Water %202007.pdf Department of Public Works and Highways (DPWH). (n.d.). Blueprints DOST XI Davao building cnr. Dumanlas and Friendship road. Davao, Philippines. DOST. (n.d.). What we do. Retrieved 09 19, 2012, from Department of Science and Technology: http://dost.gov.ph/index.php?option =com_content&view=article&catid=5 8%3Aabout-dost&id=381%3Awhatwe-do&Itemid=82#vision DPWH Davao. (n.d.). Proposed three story building DOST XI. Davao. Dr. Sales, A. (2012, 10). Rain water harvesting for new DOST Davao building. (V. Oskam, Interviewer)
http://davao.vincentoskam.nl
D.ID B.01‌. 9 of 10
Feasibility and revenue of Rain Water Harvesting Systems (RWHS) in Davao An analysis using simulation Google. (2012). Davao. Retrieved 11 4, 2012, from Google Maps: http://goo.gl/maps/yQIlS Green roof Philippines. (2012, 04 08). Rainwater harvesting. Retrieved 10 30, 2012, from http://greenroofphilippines.com/rain water-harvesting-new/ ICE Hardware shop, C. (2012, 10 15). Price of water tank (Best Tank). (V.Oskam, Interviewer) Maspinas, H. (2012, 9 12). (V. Oskam, Interviewer) Oskam, V. (2012, 10). Observation. Davao. Oskam, V. (2012, 11 01-02). Observations. Davao, Philippines. Pag-asa. (1994). Surface observation 28-021994. PAGASA FORM 1001-AB, 1. Retrieved 11 2, 2010 Texas water development board. (2005). The Texas manual on Rainwater Harvesting. Austin, Texas: Texas Water Development Board. Texas Water Development Board, Brown, C., Gerston, J., & Colley, S. (2005). The Texas Manual on Rainwater Harvesting. Austin, Texas: Texas Water Development Board. The Philippine Star. (2010, 4 18). Campaign on rain water harvesting to be launched. Philippine Star, p. 1. Vierhout, M. M. (2012). PUM Expert's Final Report on Mission Drainage of Davao. Davao City. Water Sanitation Hygiene (WASH) coalition Pilipinas. (n.d.). How to construct a ferrocement rainwater harvesting tank. Retrieved 10 30, 2012, from http://www.itnphil.org.ph/docs/How %20to%20construct%20a%20rainw ater%20harvesting%20tank.pdf WDInfo. (2011, 5 12). Davao City Water District Data. Retrieved 11 5, 2012,
Vincent Oskam, 2012
from WDInfo Water rates: http://122.54.214.222/waterrates/W DInfo.asp?CCC=5 World Health Organization (WHO). (2008). Guidelines for Drinking-water Quality. Geneva. Retrieved 12 24, 2012, from http://www.who.int/water_sanitatio n_health/dwq/fulltext.pdf
http://davao.vincentoskam.nl
D.ID B.01‌.10 of 10