Cost Efficiency
On this page, you will find the summary of the official evaluation of a Safe Water Garden (SWG) by the Indonesian government.
The evaluation was conducted in December 2019 by the Indonesian national agency vested with the authority to set and review national sanitation standards:
Puskim PU – Pusat Litbang Perumahan dan Permukiman, Bandung (Research Centre for Human Settlements, Ministry of Public Works)
The report concludes that the Safe Water Garden (SWG) meets the national standards and can be used by 1-10 families. Puskim further endorses several future research programs, notably:
- Investigating opportunities to improve the (cost)efficiency of the SWG even further
- Establishing a safe minimum distance of the well from the SWG, as this could well be lower than the currently recommended distance (10 meters) between a village sanitation system and a well
- Verifying that E. coli pollution in village wells is primarily attributable to village chickens, but that putting a lid on water wells can eliminate this problem
Why a Safe Water Garden is the most cost-efficient sanitation system for village communities
The traditional view of a septic tank
Many traditional autonomous sanitation systems worldwide utilise septic tanks.
A widely adopted consensus view of a septic tank is that it should have 2 days of “residency time” (meaning the wastewater must stay, on average, 2 days in the tank before being carried off).
For a family of 4 using 75 litres per day per person, the septic tank should be at least 600 litres. For a family of 10, the tank should have a capacity of 1,500 litres. If 5 families (each with 4 pp) share, the tank should be 3,000 litres, etc.
The tank in the SWG has a fixed size
In contrast to the above, the Indonesian government approved the SWG with a tank of fixed size (around 500 litres) for up to 10 households.
This allows the SWG to keep the cost per family very low:
Usually, the most considerable cost of simple traditional sanitation systems is the septic tank; however, in the SWG, the price of the tank is less than USD 100 and can be as low as USD 50 if the tanks are produced on a large scale.
As a consequence, if families share a SWG, the cost could be as low as USD 50 per household.
How did the Indonesian standards office approve the SWG without contradicting traditional sanitation science?
The Indonesian standards board does not regard the SWG tank as a “septic tank”. Instead, they view the tank and the garden as a single system, whereby the tank acts more as a filter that prevents system clogging (while also serving as an anaerobic reactor to reduce organics).
This way, the standards board respected traditional sanitation science, while allowing the SWG to be recognised as a sanitation system that delivered on all key fronts: health impact, biochemical performance, user satisfaction, and (cost) efficiency.