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Water Purification Packet

Water purification packets contain powdered ferric sulfate (a flocculent) and calcium hypochlorite (a disinfectant). After treating water with a water purification packet, free available chlorine is created, which disinfects and provides short-term residual protection for the water and prevents water-borne diseases. In addition, water purification packets remove arsenic, lead, and some pesticides from water. Each packet can treat 10 liters of turbid water.

Unit of interventionper packet

Formulation4 grams of ferric sulfate and calcium hypochlorite

Target populationAll ages

For information about how PSI is increasing access to water purification packets to improve health and save lives, visit our website at:
http://www.psi.org/health-area/child-health/diahhreal-disease/

Model Overview

PSI’s water purification impact model is based on the Lives Saved Tool (LiST). LiST is used to estimate the number of deaths averted with complete coverage of water purification packets in select countries. This number of deaths averted at the population level is translated to deaths averted per water purification packet, using parameters such as existing coverage of water treatment products, per capita usage of water per day, and liters of water treated per water purification packet. Once we have deaths averted per water purification packet, we apply data from the 2010 Global Burden of Disease study to estimate the corresponding number of DALYs averted.

Model Outputs (impact metrics)

Estimates of DALYs averted, deaths averted, CYPs provided, and unintended pregnancies averted represent the projected health impact of the intervention. It is projected because it has not been directly measured.

Examples based on distribution of water purification packets in Myanmar in 2015 Statement of modeled results, examples:

In 2015, an estimated 2 deaths and 136 DALYs would be averted if 10,000,000 water purification packets were distributed in Myanmar.

For more details about how PSI models the impact of water purification packets, see below.

Model Details

Step 1: Running a projection in the Lives Saved Tool (LiST)LiST is a multi-cause mortality model developed by Johns Hopkins Bloomberg School of Public Health that estimates the number of deaths averted (or lives saved) through the scale up of maternal and child health interventions.

LiST is a multi-cause mortality model developed by Johns Hopkins Bloomberg School of Public Health that estimates the number of deaths averted (or lives saved) through the scale up of maternal and child health interventions.

PSI begins by running a projection in LiST for select countries. In this projection, access to treated water is increased from the current, country-specific baseline (taken from DHS surveys) to 100%. LiST then projects the number of deaths averted among children under five by this increased level of coverage.

Step 1 Output:
Number of additional deaths averted (or lives saved) among children under five if coverage of water purification packets increased from baseline to 100% in select countries

Step 2: Estimating deaths averted per PUR packet among children under five PSI uses the step 1 output (deaths averted at 100% coverage of PUR) to determine the number of deaths averted by a single water purification packet. To do this, we divide the number of deaths averted at 100% coverage by the number of water purification packets needed to reach 100% coverage among children under five.

PSI estimates the number of water purification packets needed to reach 100% coverage using a number of parameters, including existing coverage of water treatment products, per capita usage of water per day, and liters of water treated per water purification packet. We also account for wastage of packets in the supply chain, assumed to be 10%. P2

Step 2 Output:
Under five deaths averted coefficient per water purification packet

Step 3: Estimating DALYs averted per water purification packet among children under five A DALY (or disability adjusted life year) includes two components: years of life lost due to premature death (YLL) and years lived with disability (YLD). DALYs averted are in turn comprised of YLLs averted and YLDs averted or, put simply: death and disability that is prevented by PSI interventions.

To estimate YLLs averted per water purification packet among children under five, PSI first determines the number of years of life lost per death among children under five due to diarrhea in select countries. This is equal to the life expectancy at the average age of death from diarrhea. Age specific life expectancy is taken from the 2010 Global Burden of Disease study. The number of years of life lost per diarrhea death is then multiplied by the number of deaths averted per water purification packet among children under five (under five deaths averted coefficient), calculated in step 2 above for a selected country. This gives us the YLLs averted per water purification packet.

To estimate YLDs averted per water purification packet among children under five, we use a YLD/YLL ratio, based on the 2010 Global Burden of Disease study. This ratio represents the relative number of years lived with disability for every year lost due to death from diarrhea. We apply this ratio to the number of YLLs averted per water purification packet to determine the number of YLDs averted per water purification packet among children under five.

Finally, YLLs averted and YLDs averted are added together to determine the number of DALYs averted per water purification packet among children under five.

Step 3 Output:
Under five DALYs averted coefficient per water purification packet

Step 4: Extrapolate deaths and DALYs averted among children under five to all ages Water purification packets impact individuals of all ages. In order to estimate impact at the population level, we have to extrapolate deaths and DALYs averted among children under five to deaths and DALYs averted among all ages. This is done by using two new ratios, both of which are calculated using the 2010 Global Burden of Disease study:

Step 4 Outputs:
deaths averted coefficient (all ages)
DALYs averted coefficient (all ages)