Skip to content

Cost efficiency

On this page you will find the summary of the official evaluation of the Safe Water Gardens (SWG) by the Indonesian government.

The evaluation was conducted in Dec 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 conclusion of the report is that the Safe Water Garden (SWG) satisfies the national standards, and can be used for 1 – 10 families. Puskim further endorses a number of future research programs, notably:

  1. investigating opportunities to improve the (cost)efficiency of the SWG even further;
  2. establishing a safe minimum distance of the well from the SWG, as this could well be lower than the currently recommended distance (10 meter) between a village sanitation system and a well;
  3. 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.

A copy of the full 62 page report can be found online on the Puskim website, please click here to read.

Why the Safe Water Garden is now the world’s most cost-efficient sanitation system

The traditional view of a septic tank

Many of the traditional autonomous sanitation systems around the world involve so-called 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 liters per day pp, that would mean the septic tank should be 600 liters minimum. For a family of 10, the tank should be 1,500 liters. If 5 families (each with 4 pp) share, the tank should be 3,000 liters, etc.

The tank in the SWG, however, has a fixed size

In contrast to the above, the Indonesian government approved the SWG with a tank of fixed size (around 500 liter) for up to 10 households.

This allows the SWG to keep the cost per family very low:
Normally, the biggest cost of simple traditional sanitation systems is the septic tank, but in the SWG the cost of the tank is less than USD100 and could be as low as USD50 if the tanks get produced on a large scale.

As a consequence, if families share an SWG, the cost could be as low as USD50 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”. Rather, they view the tank and the garden as one single system, whereby the tank acts more as a filter that prevents system clogging (while doing some work 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 fronts that matter: health impact, bio-chemical performance, user-satisfaction and (cost)efficiency.

Support a good cause