<P> Inevitably after events such as earthquakes and tsunamis, there is an immediate response by the aid agencies as relief operations get underway to try and restore basic infrastructure and provide the basic fundamental items that are necessary for survival and subsequent recovery . Access to clean drinking water and adequate sanitation is a priority at times like this . The threat of disease increases hugely due to the large numbers of people living close together, often in squalid conditions, and without proper sanitation . </P> <P> After a natural disaster, as far as water quality testing is concerned there are widespread views on the best course of action to take and a variety of methods can be employed . The key basic water quality parameters that need to be addressed in an emergency are bacteriological indicators of fecal contamination, free chlorine residual, pH, turbidity and possibly conductivity / total dissolved solids . There are a number of portable water test kits on the market widely used by aid and relief agencies for carrying out such testing . </P> <P> After major natural disasters, a considerable length of time might pass before water quality returns to pre-disaster levels . For example, following the 2004 Indian Ocean tsunami the Colombo - based International Water Management Institute (IWMI) monitored the effects of saltwater and concluded that the wells recovered to pre-tsunami drinking water quality one and a half years after the event . IWMI developed protocols for cleaning wells contaminated by saltwater; these were subsequently officially endorsed by the World Health Organization as part of its series of Emergency Guidelines . </P> <P> The simplest methods of chemical analysis are those measuring chemical elements without respect to their form . Elemental analysis for oxygen, as an example, would indicate a concentration of 890,000 milligrams per litre (mg / L) of water sample because water is made of oxygen . The method selected to measure dissolved oxygen should differentiate between diatomic oxygen and oxygen combined with other elements . The comparative simplicity of elemental analysis has produced a large amount of sample data and water quality criteria for elements sometimes identified as heavy metals . Water analysis for heavy metals must consider soil particles suspended in the water sample . These suspended soil particles may contain measurable amounts of metal . Although the particles are not dissolved in the water, they may be consumed by people drinking the water . Adding acid to a water sample to prevent loss of dissolved metals onto the sample container may dissolve more metals from suspended soil particles . Filtration of soil particles from the water sample before acid addition, however, may cause loss of dissolved metals onto the filter . The complexities of differentiating similar organic molecules are even more challenging . </P>

The one measure that can tell the most about the overall quality of a surface water source is