As Bali faces an increasing water crisis, with over-drilling of bore wells and seawater intrusion, it’s time to rethink how we source our water. The good news is, there’s a free and pure alternative right above us: rainwater. Rainwater harvesting is not just an eco-friendly trend; it’s a practical necessity for sustainable living in Bali.
Why Harvest Rainwater?
- Pure and Natural: Rainwater is essentially distilled water, soft, and free of bacteria and mineral contaminants. It’s the purest form of water available naturally.
- Free Resource: Unlike groundwater, which requires costly extraction and filtration, rainwater is free for the taking.
- Reduced Environmental Impact: By collecting rainwater, you reduce the demand on Bali’s strained water table, helping to combat the ongoing water crisis.
- Avoid Contamination: Groundwater is often contaminated by dead animals, fertilizers, chemicals, septic tank leakages, and heavy metals. Rainwater harvesting bypasses all of that.
Is Rainwater Harvesting Viable? Absolutely!
A well-planned rainwater harvesting system is both viable and practical for most homes. Here’s what you need:
- Gutters: Install 8-inch wide box gutters with strong mounting brackets, spaced no more than 60 cm apart, around your roof to collect rainwater. Make sure to install downpipes that are a minimum of 4 inches in diameter, but preferably 6 inches.
- Storage Tanks: Depending on your needs, opt for either plastic tanks (5,000 liters each is a good starting point), or an underground reinforced concrete tank. Plastic tanks should be kept out of sunlight to prevent damage, and avoid burying them since they may pop up if the ground is saturated with water. Concrete tanks need to be able to withstand earth tremors.
- Flushing System: Incorporate a system that allows the initial rainwater runoff to bypass your collection system, ensuring that your water is free from roof debris, bird droppings, or volcanic ash.
- Filtration: Basic filtering is a good idea to ensure the water is clean. You can include a UV filter to eliminate bacteria and a sand filter to remove dirt.
Calculating Your Needs
To create an effective rainwater harvesting system, you will need to consider how much water you need, how much you can collect, and how much to store.
- Water Usage: An average couple can expect to use around 170 liters of water per day or 62,000 liters per year if careful with their usage.
- Water Collection: Denpasar receives an average of 1,650 mm of rain annually, which translates to 1,650 liters per square meter of roof area. So, a 60 square meter roof can collect approximately 98,000 liters per year.
- Storage: Sufficient storage is crucial to get through dry periods. Consider having enough storage to last through dry periods by planning your water needs with your collection capacity.
Example: Based on a couple using 220 liters of water per day with a roof area of 60 square meters, here is a sample calculation of monthly water storage needs:
| Month | Rainfall (mm) | Rain Collected (ltr) | Water Usage (ltr) | Balance Water Stored (ltr) |
|---|---|---|---|---|
| January | 323 | 19,380 | 6,820 | 12,870 |
| February | 251 | 15,060 | 6,160 | 22,050 |
| March | 199 | 19,380 | 6,820 | 27,480 |
| April | 89 | 5,340 | 6,600 | 26,520 |
| May | 86 | 5,160 | 6,820 | 25,170 |
| June | 75 | 4,500 | 6,600 | 23,370 |
| July | 67 | 4,020 | 6,820 | 20,880 |
| August | 47 | 2,820 | 6,820 | 17,190 |
| September | 46 | 2,760 | 6,600 | 13,650 |
| October | 117 | 7,020 | 6,820 | 14,160 |
| November | 162 | 9,720 | 6,600 | 17,580 |
| December | 179 | 10,740 | 6,820 | 21,810 |
Additional Tips for Success
- Water Meter: Install a water meter after the supply pump to monitor water usage.
- Rain Gauge: Keep an eye on rainfall with a rain gauge to compare expected collection with actual usage and identify any potential leaks.
- Tank Access: Design your tanks with access for cleaning, and ensure any underground tanks have manholes without light entry.
- Recycle: Consider recycling grey water for garden use to minimize your overall water consumption.
Make a Difference With Rainwater Harvesting
Rainwater harvesting is more than just a trend; it’s a crucial step towards water sustainability in Bali. By implementing a well-planned system, you’re not only securing a reliable water source for your home, but you’re also contributing to the overall health of the island’s ecosystem.
