Rainwater Harvesting System

Sizing The Tank

For those who are interested in installing a similar rainwater harvesting system for their homes (Kuala Lumpur area only). Tangki NAHRIM is available for download to size the rainwater storage tank based on daily water usage and daily rainfall.

User's Guide:

Step by step guide for using Tangki NAHRIM

1. The software maybe run from the diskette or hard disk. Wherever the software is run from, the command line is "drive name : Tangki NAHRIM 1.0.exe". File "vbrun100.dll" is needed to run Tangki NAHRIM 1.0.exe and both file should be in one folder.

2. The starting screen (Figure 1) is where the user needs to specify the following parameters:

1. The roof characteristics such as the length and width of roof, the run-off coefficient which depends on the material of the roof and the first flush volume which accounts for the amount of water needed to wash the roof with each rainfall before the remaining rain water can be used.
2. The water usage characteristics which include the number of persons using the water, the volume used per person and the size of storage tank used for the rain water.
3. Rainfall areas: at present, the software only includes data of rainfall for the Kuala Lumpur area as recorded at the DID Ampang station. Rainfall data for other selected areas will be included in future.

3. In the starting screen, the user have the following options: 

1. For simulating with the monthly data, the user may proceed directly to the simulation menu by clicking the "Continue" button or may choose to look at the rainfall data ("View R.F. Data"). The rainfall data is given in a tabulated form for the years 1983-1997.
2. For simulating with the daily data, the "Simulate Daily" button will bring the user to the screen which displays the daily rainfall data. The "Show Data" button will display the data for each month in the table. Repetitively clicking this button will display the data for the following months. Alternatively, the user may specify the particular year, then the data for that year will be displayed in a consecutive manner. Choosing "Continue" will bring the user to the Simulation Menu.
3. The "Display Updates" button is for displaying the latest values specified by the user for each parameter when returning from the Simulation Menu after changes are made to these values which are different to the default values.
4. The "Return" button is for the user to go directly to the Simulation Menu after making changes to the values of the parameters.
5. The "Print Form" button will print this form using the default printer and the "End" button will end the program.

4. In the Simulation Menu (Figure 2), the user have the following options:

1. To run the software with the monthly data, either choose "Fast Simulation" or "Slow Simulation". Fast simulation is for getting the results quickly while slow simulation is for observing the simulation progress at a slower phase. While the simulation is run, the user is shown the conditions of water in the storage tank plus the following information:
   1. Total rain water volume delivered.
   2. Number of days the demand or usage volume not fully met.
   3. Number of days with no rain at all.
   4. Number of days when there is no rain and the storage tank empty.

Figure 2: The simulation screen

At the end of each simulation run, the following information are provided:

1.  
   1. The reliability ratio.
   2. The percentage of the total time that the storage tank became empty.
   3. The total volume of rainwater collected and delivered to the user.
   4. The average volume of rainwater delivered per day.

The user is also provided with the following analysis results by clicking the respective buttons:

1. The "Analysis Results" button will show the total rainwater captured by the system, the coefficient of rainwater utilization and the storage efficiency.
2. The "Monthly Results" button will display the reliability values for every month from January to December.
3. The "Tank Condition" button will show the percentage of the time that the water level in the tank at the different levels i.e. full, three quarters, half, one quarter and empty.

1.  To run the software with the daily data, the user should choose "Fast Simulation" or "Slow Simulation" button in the "Daily Simulation" frame. Again, fast simulation is for getting the results quickly while slow simulation is for observing the simulation progress at a slower mode. 
2. The "Print Results" button is for printing the daily output for the rain water volume delivered, water level in the tank and ratio of water demand met in a month. For this, the user needs to specify the month and year for which the results are required.

5. When the "Graphic Display" button is chosen, the user is shown the Graphic Display Screen. In this screen, the user can observe the daily fluctuations of the water level in the storage tank for one month at a time for the 15 years period. The following options are available:

1. "Fast Simulation" is for getting quick results with the monthly data.
2. "Slow simulation" is for observing the simulation at a slower phase.
3. "Daily Data" simulation will run the model using the daily rainfall data.
4. "Specific Month" enables the user to specify to view which particular month.
5. "Step Simulation" displays the results for the following month.

6. The "Change Parameter" button is for going back to the Starting screen where the user may change the values of the parameters for subsequent simulations.

7. Every form in the software is provided with the "Print" or "Print Form" buttons that enable printing of individual forms to be done. Also, "End" buttons are provided for quick exit from the program.

System Design

Various subsystem of the rainwater harvesting system is shown below:

(i) Catchment’s Subsystem

The rooftop is the catchments subsystem. For non-potable use, any roofing material can be used as the catchments subsystem. As for potable use, the best roof materials are metal, clay, and cement materials although all roof material types have been used (except asbestos). The roof material used in the study is of cement tiles.

Catchments subsystem depends on the roof configuration of the house. In this study, due to the typical roof design, only the front section of the house is considered. The total roof area is 60 m.

(ii) Conveyance Subsystem

The function of this subsystem is to convey the rainwater from the catchments sub-system (rooftop) to the storage tanks. Basically this subsystem consists of 3 main components. These components are the gutter, downpipes and the conveyance pipes. Rainwater from the rooftop is channeled to the gutters (6" or 150mm) and then through the downpipes and finally through the conveyance pipes to the storage tanks.

Aluminum and galvanized iron are usually the best materials for the gutter due to its good corrosion resistance property. For the conveyance pipes, usually UPVC pipes are used. However in this study, UPVC type materials were used as gutter and conveyance pipe due to their flexibility during installation. The gutter slopes at 6 mm. per meter and gutter hangars are provided at 1 m center to center.

At the downpipe inlet a net should be placed. The net is to trap rubbish, leaves and other debris usually found on rooftops. Sharp bends along the run of the gutters should be avoided. This is because, rubbish usually gets stuck at corners and therefore this would affect the flow of the rainwater.

(iii) Filtration

Rainwater from the rooftop (the first 1 mm of rain) is usually contaminated with dirt, bird droppings, leaves and other materials. The first flush (60 gal. or 276 litres) of rainwater from the roof surface is directed into the first flush tank of 200 litres (see figure below) to filter out these materials from the rainwater before it is stored in the storage tanks.

(iv) Storage Tank

In this study, two number of PVC tanks (see figure below) with a 2500 litres capacity each were installed as storage tanks.

(v) Booster pump

A 1.0 horsepower pump (see figure below) with minimum head of 12 m was installed to

(vi) Roof tank

Additional roof tank (250 litres) were installed on the roof in addition to the existing domestic roof tank. The additional tank provide separate rainwater supply for non-potable household use.

(vii) Plumbing to toilets, washing machine and general use

The study house also has a separate plumbing system to cater for rainwater usage. Since rainwater was for non-potable use, the plumbing system was installed in such a way that there will be a bypass connection for each flushing cistern. In case of water shortage or non-availability of rainwater, the public water supply can be always be switched on. The rainwater plumbing system also connects to the washing machine pipe and pipe for general cleaning.

Rainwater pipe connection to toilet		Rainwater pipe for washing machine		Rainwater pipe for general cleaning

Please click to enlarge image

Water Quality Aspects

Samples of the quality of rainwater collected in the storage tank are analysed and compared with World Health Organisation (WHO) Drinking Water Quality Guidelines (see Table 2). The results show that the pH which ranges from 6.26 to 6.62 is reasonable. The hardness at between 8.6 to 32.6 is low. The manganese and iron contents are low as well. Toxic metals such as cadmium at less than 0.001 mg/l is below the WHO Guideline while lead at < 0.05 mg/l is above the WHO Guideline. The Faecal Coliform at 20 counts per 100 ml shows contamination from some animals.

Table 1 shows average water use for facilities using rainwater based on twelve months data. Since there was no treatment to the rainwater collected, therefore it is strictly used for toilet flushing, general cleaning and washing clothes.

Water Usage

Cost

Benefits