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Updated March 29, 2017

Project Impact By Country

Learn about PSI's models

# Safe Water Solution

## Model Overview

**Model Outputs**
**Examples based on distribution of safe water solution in Myanmar in 2015**
**Statement of modeled results, examples:**

*In 2015, an estimated 2 deaths and 136 DALYs would be averted if 100,000 150mL bottles of safe water solution were distributed in Myanmar.
*
## Model Details

**Step 4: Extrapolate deaths and DALYs averted among children under five to all ages**Safe water solution impacts 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:

Safe Water Solution, often marketed as WaterGuard or Sur’Eau, is a 1.25% concentration of sodium hypochlorite solution, point-of-use water treatment product that is used to disinfect water and prevent water-borne diseases. It is a simple to use, inexpensive, and effective method for households to disinfect their own water. Each capful (3mL) will treat 20L of clear water.

**Unit of intervention**per bottle (size is brand dependent)

**Formula**1.5% sodium hypochlorite (NaOCl) per bottle

**Target population**all ages

For information about how PSI is increasing access to safe water solution to improve health and save lives, visit our website at:

http://www.psi.org/health-area/child-health/diahhreal-disease/

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

- Deaths averted per bottle of safe water solution
- DALYs averted per bottle of safe water solution

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.

- 2015 Deaths averted per 150mL bottle of safe water solution: 0.000020
- 2015 DALYs averted per 150mL bottle of safe water solution: 0.001364

For more details about how PSI models the impact of safe water solution, see below.

**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.

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 safe water solution increased from baseline to 100% in select countries*

**Step 2: Estimating deaths averted per bottle of safe water solution among children under five**PSI uses the step 1 output (deaths averted at 100% coverage of safe water solution) to estimate the number of deaths averted by a single safe water solution bottle. To do this, we divide the number of deaths averted at 100% coverage by the number of bottles needed to reach 100% coverage among children under five.

PSI estimates the number of safe water solution bottles 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 unit of safe water solution. We also account for wastage of safe water solution in the supply chain, assumed to be 10%.

*Step 2 Output:*

*Under five deaths averted coefficient*

**Step 3: Estimating DALYs averted per bottle of safe water solution 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 safe water solution bottle among children under five, PSI first estimates 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 safe water solution bottle 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 safe water solution bottle.

To estimate YLDs averted per safe water solution bottle 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 safe water solution bottle to estimate the number of YLDs averted per bottle among children under five.

Finally, YLLs averted and YLDs averted are added together to estimate the number of DALYs averted per safe water solution bottle among children under five.

*Step 3 Output:*

*Under five DALYs averted coefficient*

- Ratio 1: Number of deaths among children under five / deaths among all ages
- Ratio 2: Number of DALYs among children under five / DALYs among all ages

Each ratio is applied to its respective impact coefficient (deaths or DALYs averted among children under five per safe water solution bottle) to estimate the number of deaths and DALYs averted among all ages.

*Step 4 Output:*

*Deaths averted coefficient (all ages)*

*DALYs averted coefficient (all ages)*