Most commercial and industrial buildings in Indonesia treat water as an unlimited input with a small bill attached. That assumption is weakening: groundwater extraction is more tightly controlled, dry season restrictions are more common, and tariffs continue to rise. Meanwhile, buildings discharge rainwater to drainage and treated wastewater to rivers, then buy clean water for uses that never needed drinking quality.
Rainwater harvesting
Indonesia’s rainfall makes harvesting straightforward in principle: a roof, gutters, a first-flush diverter to discard the dirtiest initial runoff, filtration, and storage. The design questions are about sizing and use.
- Catchment area and rainfall pattern determine how much you can collect, and how long the dry-season gap is that storage must cover.
- End use determines treatment. Landscape irrigation and cooling tower make-up need far less treatment than washing or process water.
- Storage is the cost driver. Oversized tanks sit empty; undersized tanks overflow in the wet season and run dry in the dry one.
- Recharge is a legitimate outcome. Where storage is impractical, infiltration wells and biopori return water to the aquifer and reduce local flooding.
Water reuse and recycling
Reuse takes water that has already been used and returns it to service. Greywater from wash basins and condensate from air conditioning systems are the easiest sources. Treated effluent from a wastewater treatment plant can be recycled where the treatment train and monitoring support it.
The rule is to match quality to purpose. Flushing, irrigation, cooling tower make-up, and floor washing do not require potable water, and in a typical commercial building they represent a substantial share of demand.
Where the value shows up
- Lower utility cost and reduced dependence on groundwater extraction permits.
- Operational resilience when restrictions or supply interruptions arrive.
- Certification credit under Greenship, EDGE, and LEED water categories.
- Compliance headroom, since reducing discharge volume eases the load on your wastewater treatment plant and your Pertek PMBAL obligations.
- Reportable performance, as water withdrawal and discharge are disclosure indicators under GRI and most ESG frameworks.
Designing it properly
A water strategy begins with a water balance: how much comes in, where it goes, and at what quality each use actually requires. From there the system is sized against real demand rather than a rule of thumb. Two details decide whether it survives: dual plumbing with clearly marked non-potable lines, and a maintenance plan for filters, tanks, and first-flush devices. Harvesting systems rarely fail structurally. They fail because nobody cleaned the filter.
A quick sizing example
Consider a commercial building with 2,000 square metres of roof catchment in an area receiving 2,000 mm of rainfall a year. Applying a runoff coefficient of around 0.8 to account for losses, the theoretical yield is roughly 3,200 cubic metres a year, or an average of 267 cubic metres a month.
If landscape irrigation, toilet flushing, and floor washing together consume about 10 cubic metres a day, harvested rainwater could cover a meaningful share of that demand through the wet season. Storage, however, is not sized for the whole dry season. A tank large enough to carry several months of demand is rarely economical. A more typical approach is to size storage for one to two weeks of demand, around 100 to 150 cubic metres in this example, and to treat mains or groundwater as the backup during extended dry periods.
The numbers change with roof area, rainfall pattern, and end use, which is why a water balance comes before tank selection rather than after it.
How Aruni Architecture & Green Design can help
We design wastewater treatment plants for domestic and industrial applications, water recycling and reuse systems, and rainwater harvesting and building water management, integrated with green building certification and environmental compliance so one system satisfies both.
See our environmental engineering and clean water services or talk to our team.
