This is almost too simple to be real. And it makes you wonder... why did this take so long?
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Using the sun to sterilise water
Tanzanian villagers have begun using an energy-saving method to sterilise their drinking water - leaving the water under the sun.
The piped water supply to Ndolela village in the central Iringa region is intermittent and even when it does it flow, it is not clean enough to drink.
When the pipes run dry, villagers get water from a dirty spring.
Mother of five Rose Longwa says the new process has changed her life.
"We no longer suffer from stomach illness. That's because the water is clean and safe."
Like many other people in rural Africa with no access to safe drinking water, she used to sterilise her water by boiling it.
But she says the smoke from the firewood to heat the water used to irritate her eyes. She is also glad she no longer has to go to fetch wood from the bush.
About 40 houses in Ndolela are using solar purification.
Mrs Longwa says the process is simple to follow.
We need to educate the people
"I fill the plastic bottles, put the lids on, then put them on my black-painted roof where they stay for a whole day."
The sun heats the water, helped by the black roof, which helps to absorb the heat.
Solar radiation means a combination of ultra-violet rays and heat destroys the bacteria which cause common water-borne diseases like cholera, typhoid, dysentery and diahorrea.
After eight hours in the sun, it is ready to drink.
If the water reaches more than 50C, it is safe in just one hour.
Pastor Moses Kwanga from the Diocese of Ruaha is behind the project:
"The technology is very easy, but up to now people have not been told about it. We can use old pieces of roofing to put the bottles on. It is also very cheap, so is accessible to everyone."
Up to now, the number of people in Tanzania purifying water using the power of the sun is limited to a few villages like Ndolela, where small-scale education programmes are underway.
Daudi Makamba is a water expert for the aid agency Plan International, which is considering whether to introduce solar purification across the country.
He says it can be difficult to persuade people to use the technology.
"The big resistance from the community is cultural beliefs. People believe the water will be contaminated, or an enemy will put something bad in it, so we need to educate the people."
The technology is working well for at least one community in Tanzania but more work is needed if more people are to taste the benefits.