Traditional dry vault toilet systems have been around for centuries in Central Asia and parts of China where nutrients for agriculture are scarce. However, some analysts say they are inappropriate for urban areas, as they pose a threat to public health.
Most urban households in Afghanistan use specially-shaped dry vault toilets which collect solid and liquid waste separately.
Dry vault toilets can be safe and they provide a ready-made fertiliser for urban agriculture, supporters say.
When Kabul was a small town, sanitation experts say, it was feasible and safe for donkey carts to carry excrement out of town for use as fertiliser. However, rapid urbanisation is putting this traditional practice into question.
Dry vault systems catch and store solid waste in a separate chamber from urine and are sometimes referred to as "ecological sanitation" systems - and have significant advantages in some situations, a sanitation analyst working on the issue told IRIN. The "night soil" in the dry vault can be removed and carried away and used as fertiliser.
Sanitation consultant Barbara Evans said that the alternatives, flush toilets connected to a piped sewage system, or pit or soakaway latrines had their own problems.
"Sewered sanitation is very costly to build and prohibitive to run because of lack of water and power... This provides flush toilets for development agency staff, government offices, etc, but I am not sure that it's an option for the whole city - it's just too costly," Evans told IRIN.
Pit latrines and septic tanks also fill up and their contents have to be disposed of, while pit latrines can seep into groundwater, contaminating wells, especially where the water table is close to the surface and where soils are sandy.
"I believe that you have to make appropriate use of technology and so far no one has shown me a more appropriate option than dry vaults for many parts of Kabul," Evans said.
Adapting traditional ecological sanitation is among the approaches that donors and aid agencies support.
According to Abdul Karim Mirzazada, country representative for the German aid organisation, German Agro Action, different kinds of projects have been implemented in Kabul, Kunduz and Takhar provinces.
One project uses water to flush faeces either to a septic covered vault (on sandy ground) or to an absorbing latrine. In another project, people defecate into a dry vault which can be emptied.
Evans said: "These days some donors are actively promoting variations on these types of latrines - commonly clustered together under the term 'ecological sanitation' to capture the idea that waste products are not wasted and do not pollute the downstream ecosystem but are kept 'in the loop' at the local level. They aren't common [internationally] and they're not always appropriate but for many people living in Kabul they are totally familiar and normal."
Urban sanitation needs
There are only 36 public toilets in Kabul, which has a population of over four million, according to Kabul Municipality.
Many resort to defecating and urinating in public places, including the River Kabul in the heart of the city, now dry due to a prolonged drought.
Photo: Akmal Dawi/IRIN
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"We believe there is an urgent need for a thorough modernisation of private and public toilet systems in Kabul," said Mohammad Yaseen Hilal, deputy director for policy and coordination in Kabul municipality.
Given the widespread use of underground water for all purposes in Kabul - where only a small fraction of houses have tap water - the municipality has warned that if all houses used septic and/or absorbing latrines that would "undoubtedly contaminate sources of water".
"An ideal solution for our toilet crisis is the establishment of a public sewage recycling system or several fragmented systems," said Hilal, but doubted his impoverished country could afford the systems in the foreseeable future.
Some blame dry toilets for foul smells in Kabul's dusty streets and for contributing to the spread of disease.
"Up to 70 percent of patients who visit hospitals for diseases such as diarrhoea are affected by unhygienic toilet facilities," said Abdullah Fahim, spokesman for Afghanistan's Ministry of Public Health.
Attaullah Ehsan, a doctor at a public hospital for infectious diseases in Kabul, said 100-150 children visit the hospital each day complaining of diarrhoea.
"Children are particularly vulnerable to parasites found in human excrement," Ehsan said, adding that sources of risk were excrement around outside toilets, and particles of dried excreta blown around by the wind. Another risk was flooding which often caused contamination of water sources.
System under strain
For dry vault systems to work, the waste needs to be handled carefully but most importantly, there needs to be a market for the waste and resultant fertilizer. That market may now be shrinking.
A 2005 study by authors from the University of Loughborough in the UK and Action contre la Faim stated that farmers with land on the outskirts of the city were selling up (at high prices) as the city expanded and so no longer needed to buy fertiliser.
The report also said the main challenge for aid agencies and government was what to do about the estimated 60 percent of the population living in unplanned shanty towns, adding that donor focus on rural areas contributed to growing inequalities in the city in terms of sanitation.
Evans said: "I would tend to ask those people who say the city is too big [for dry vault systems] to consider what the alternatives are. Few major cities with the growth and poverty profile of Kabul do a good job of designing sanitation which works for the poor - they tend to spend money on expensive infrastructure that at best provides a high level of service for a tiny minority of the city - usually the elite.
"Kabul has a system which used to work - we should not abandon it unless we really have a better option to suggest that is cheap and simple enough to put in place rapidly."