The meaning of this statement is that, in terms of reducing disease, sanitation interventions have been found to be more effective than interventions which increase the quantity of water available, which, in turn, have been found to be more effective that those which address water quality.
Given even more recent studies, the statement might reasonably be amended to say Hygiene > Sanitation > Water QAUNTity > Water QUALity; because hand washing and other hygienic practices have sometimes been found to be even more effective than latrines.
These notions are counter intuitive, but an explanation can be found in transmission routes. Most of these diseases are transmitted from feces to the mouth, through the "fecal oral route". When we consider that, in addition to water, other mechanisms such as food, flies, and dirty hands also transmit these pathogens, it is easy to see that by containing fecal waste, and washing hands, more transmission routes can be broken than by disinfecting water. In the diagram below, it is possible to see that latrines (sanitation) and hand washing intervene close to the source, before the general environment can be contaminated.
There is another factor that decreases the effectiveness of providing clean water;that is recontamination. Even if people could be infected only through drinking water, in an environment that is generally contaminated with human waste, clean water can soon be contaminated by contact with dirty hands or containers. See Keeping clean water clean in a Malawi refugee camp: a randomized intervention trial. Roberts L, Chartier Y, Chartier O, Malenga G, Toole M, Rodka H. Bull World Health Org (2001) 79(4) p280-7.
Studies that lead to or supported the "Central Paradigm" are:
Esrey, S.A., "Effects of improved water supply and sanitation on ascariasis, diarrhea, dracunculiasis, hookworm infection, schistomiasis, and trachoma." Bulletin of the World Health Organization 69 (5) 1991: 609-621
Esrey,S.A., "Water waste and well-being: a multicountry study". Am J. of Epi. 1996:143(6):608-23.
Huttly S.R.A.; Morris S.S.;. Pisani V "Prevention of diarrhoea in young children in developing countries." Bulletin of the World Health Organization, March-April 1997:75 (2): p163(12)
People often think of clean water as the primary means of preventing water borne disease. Only in the last dozen years have studies begun to turn that old understanding on it's head. Now it's generally accepted that no water program should be without a sanitation and hygiene education.
Below is a chart which appears on a World Bank Group web site called "Water and Sanitation at a Glance"
The acceptance of the idea is also reflected in publications of:
SPHERE, from the SPHERE Minimum Standards in Disaster Response
"Proper disposal of human excreta creates the first barrier to excreta-related disease, helping to reduce disease transmission through direct and indirect routes. Excreta disposal is therefore a first priority, and in most emergency situations should be addressed with as much speed and effort as water supply."
"In most cases .. the main health problems associated with inadequate water supply are caused by poor hygiene due to lack of water, and by the consumption of water that is contaminated at some stage."
"Until minimum standards for both quantity and quality are met, the priority should be to provide equitable access to an adequate quantity of water of intermediate quality, rather than to provide an inadequate quantity of water which meets the minimum standard for quality."
UNHCR, from the UNHCR Handbook for Emergencies,page 216
"In order to be effective, water quality control and treatment have to be combined with improved personal hygiene and environmental health practices...The water supply system design and construction must be ...supported by health, education and environmental measures, in particular sanitation."
2.If there is an epidemic, and a contaminated water source is suspected, water QUALity interventions become more important than water QUANTity.
3.(from the SPHERE Handbook) "Progress in achieving standards in one area determines the importance of progress in other areas. For instance, in situations where excreta disposal and hygiene facilities are inadequate, it is more urgent to reach the minimum water quantity standard than in situations where the environment is relatively free of pathogens due to adequate sanitation and hygiene conditions."
2. Adequate "Water quantity" refers not just to drinking water, but to water available for hand washing, bathing, laundry, etc. 3. The term "Sanitation" has various definitions. On this site it means the containment and disposal of human waste.
2. If there are other studies which have not been mentioned here
(which support the San > Quantity >Quality) I'd very much like to hear of those as well.
MERLIN Medical Emergency Relief International http://www.merlin.org.uk/Lists/News-Detail.aspx?id=429
WSSCC Water Supply and Sanitation Collaborative Council http://www.wsscc.org/
IRC International Water and Sanitation Centre http://www.irc.nl/page/10524
Water for People http://www.waterforpeople.org/
WHO World Health Organization http://www.who.int/water_sanitation_health/en/
Waterlines http://practicalactionpublishing.org/?id=waterlines International journal of appropriate technologies for water supply and sanitation
EHP Environmental Health Project http://www.ehproject.org/
The Sanitation Connection http://www.sanicon.net/index.php3
UNICEF United Nations Children's Emergency Fund http://www.unicef.org/wes/
BPD Building Partnerships for Development http://www.bpd-waterandsanitation.org/