The health consequences of inadequate water and sanitation services include an estimated 4 billion cases of diarrhea and 1.9 million deaths each year, mostly among young children in developing countries.  Diarrheal diseases lead to decreased food intake and nutrient absorption, malnutrition, reduced resistance to infection, and impaired physical growth and cognitive development.  Since 1996, a large body of published work has proven the effectiveness of interventions to improve water quality through household water treatment and safe storage (HWTS) at reducing diarrheal disease.  However, not all of these interventions remove the turbidity that causes water to look dirty.  Although the following options are not proven to reduce diarrheal disease incidence on their own, they can be used to pre-treat water to reduce turbidity before the use of household water treatment products.  These options mechanically (through filtration) or chemically (through flocculation and settling of suspended material) remove particles and reduce turbidity.  These pre-treatment methods may also increase the efficacy of household water treatment products by removing contaminants that interfere with disinfection and physical filtration processes. 

Flocculation is a process which clarifies the water. Clarifying means removing any turbidity or colour so that the water is clear and colourless. Clarification is done by causing a precipitate to form in the water which can be removed using simple physical methods. Initially the precipitate forms as very small particles but as the water is gently stirred, these particles stick together to form bigger particles - this process is sometimes called flocculation. Many of the small particles that were originally present in the raw water adsorb onto the surface of these small precipitate particles and so get incorporated into the larger particles that coagulation produces. In this way the coagulated precipitate takes most of the suspended matter out of the water and is then filtered off, generally by passing the mixture through a coarse sand filter or sometimes through a mixture of sand and granulated anthracite (high carbon and low volatiles coal).

Over the last 30 years a significant number of water and sanitation projects have been implemented in developing countries and billions of dollars has been spendt. Projects have covered rural as well as urban water supply systems, wastewater collection, disposal and treatment systems, and have mainly been financed by international funding agencies such as international banks and international aid organisations. However, unfortunately it is a fact that the number of failures, or non-functioning, of the established systems, outnumbers the number of successes.

Sludge is a residual, semi-solid by-product left from industrial or refining processes. It is a separated solid suspended in a liquid, typically containing major quantities of interstitial water between its solid particles. This material can be dried to cut its volume and reduce most of the moisture content of the biosolids present in the sludge.