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| Various subsystem of the rainwater harvesting system is shown below: |
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(i) Installation Cost For Rainwater Harvesting System
System cost include supply and installation and varied accordingly depending to the type of materials used. |
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Amount (RM)
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| Gutter (uPVC) |
|
150.00
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| Conveyance System |
|
200.00
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| Plumbing works |
|
400.00
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| Water tank (top) |
1 No |
200.00
|
| Water tank(ground) 2500 litres capacity |
2 Nos |
1000.00
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| Water pump(electrical) |
|
750.00
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| TOTAL |
|
RM 2700.00
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(ii) Maintenance of the system
Maintenance included cleaning of the rainwater collection system, electricity bills and chemicals to prevent mosquito breeding in the storage tank. The maintenance cost is believed to be quite small and therefore not included in the subsequent calculations.
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| (iii) Payback Period |
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| Old Tariff |
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| System Cost |
: |
RM 2700.00 |
| Water Saving/month |
: |
8940 litres x RM 1.05/m³ = RM 9.39 |
| Payback Period |
: |
RM 2700.00 / (RM 9.39 x 12) |
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24 Years |
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| New Tariff |
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| System Cost |
: |
RM 2700.00 |
| Water Saving/month |
: |
8940 litres x RM 1.70/m³ = RM 15.20 |
| Payback Period |
: |
RM 2700.00 / (RM 15.20 x 12) |
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14.8 Years |
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| * An increase of 60% water rate (>35 m3 / month) |
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(iv) Unit Cost of Water by Rainwater Harvesting
Unit Cost of water by rainwater harvesting system can be calculated using simple formula below:
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| Cost per 1000 litres |
= |
Cost of the system x 0.10 |
| Yield in litres per day x 0.365 |
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| Allowing about 10% of the capital cost to cover interest and depreciation each year |
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| For the Double Storey Terrace |
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| Average yield per day : 298 litres |
| Cost per 1000 litres |
= |
RM 2700 x 0.10 |
| 298 x 0.365 |
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= |
RM 2.48 compared to Water Supply Department (JBA) rate of RM1.05* (Old Tariff) and RM1.70** (New Tariff) |
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* > 35 m³ and above per month |
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** > 40 m³ and above per month |
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| From the above it can be seen that the unit cost of water from the rainwater harvesting system at RM 2.48/m³ is still more costly compared with the piped water cost of RM 1.70/ m³. As practiced in Japan and elsewhere the Government may need to provide subsidies to encourage the public to install rainwater harvesting systems. |
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