Introduction

Welcome to The Nonlinear Library, where we use Text-to-Speech software to convert the best writing from the Rationalist and EA communities into audio. This is: Clean Water - the incredible 30% mortality reducer we can't explain, published by NickLaing on November 4, 2023 on The Effective Altruism Forum.
TLDR: The best research we have shows that clean water may provide a 30% mortality reduction to children under 5. This might be the biggest mortality reduction of any single global health intervention, yet we don't fully understand why it works.
Here I share my exploration of a life-saving intervention that we don't fully understand,
but really should.
I may err a little on the side of artistic license - so if you find inaccuracies or I'm a bit loose please forgive me, correct me or even feel free to just tear me to shreds in the comments ;).
Part 1: Givewell's Seemingly absurd numbers
I first became curious after a glance at what seemed like a dubious GiveWell funded project. A
$450,000 dollar scoping grant for water chlorination in Rwanda?
This didn't make intuitive sense to me.
In Sub-saharan Africa diarrhoea causes 5-10% of child mortality. While significant, the diarrhea problem continues to improve with better access to medical care, improving ORS and Zinc coverage, and antibiotics for more severe cases. Over the last 5 years, our own Ugandan health centers have encountered surprisingly few very sick kids with diarrhoea and I've hardly seen diarrhoea kill a child, as opposed to Malaria and Pneumonia which tragically kill kids all the time. It seemed to me that even if clean water hugely reduced diarrhoea mortality, the intervention would still likely be an expensive way to achieve 1 or 2 percent mortality reduction,
So with my skeptic hat on, I clicked the
GiveWell spreadsheet
and my incredulity only grew. GiveWell estimated an upper-bound mortality reduction of an almighty
17%
for the Rwandan chlorination program! At first that made no sense, but I did expect GiveWell would likely be lesswrong than me.
The Global burden of disease estimates that Diarrhoea makes up only
4.9%
of total deaths in Rwanda. How could an intervention which targets diarrhoea reduce mortality by over three times the total diarrhoea mortality? Even if the clean water cured all diarrhoea, that wouldn't come close to GiveWell's mortality reduction estimate.

Something fishy was afoot, but I quickly found some answers, through a nobel prize winner's study which was partially funded by you guessed it……..
GiveWell
Part 2: A Nobel Prize winner's innovative math
Michael Kremer won a Nobel prize along with two J-PAL co-founders for their wonderful work pioneering randomised controlled trials to assess development interventions. What better person to try their hand at estimating the mortality benefit of clean water than a father of the RCT movement?
But connecting clean water and mortality is tricky, because to date no-one has actually asked whether clean water can reduce child mortality. Instead, a number of RCT asked the more obvious question,
does clean water reduce diarrhoea.
The answer obviously yes.
But Kremer and co. found a clever way around this. They sifted through all studies which looked at the relationship between clean water and diarrhoea and identified 12 studies
[1]
that also gathered bits and pieces of mortality data. They then performed a meta-analysis, pooling that mortality data together to see whether clean water save kids' lives.
The result - they estimated that clean water caused an
incredible 30% mortality reduction
in kids under 5. If this is even in the ballpark of correct, clean water could could prevent one in three childhood deaths in much of sub-saharan Africa. If Africa could chlorinate and filter all drinking water, we could save perhaps
1 million lives
every year
in sub-saharan Africa alone
.
Mosquito nets might bow to their new king.
To be as crystal clear as the water, this is not just a 30% reduction in diarrheal death...