As Britain endures one of its driest years on record, it feels absurd that so much of our rainfall still runs uselessly down the drain. Rainwater harvesting and storm-water tanks should clearly form part of the solution to the water crisis.
Australia shows what that looks like in practice. Over a quarter of Australian households have a rainwater tank, providing an estimated 274 billion litres of water a year – more than 10 per cent of all residential supply – saving the country around half a billion Australian dollars in municipal water costs annually. By comparison, the nation’s largest desalination plant cost AU$3.5 billion just to build and produces 150 billion litres a year.
And if comparing the UK and Australia seems unfair, given the former’s wet reputation and the latter’s dry one, then consider the riddle that Australian water engineer (now at Thames Water) Andrew Tucker posed to me: “Which Australian state capital city gets more rain on average every year than London?” I guessed Sydney. Nope, he said. “They all do.”
Mexico City is another modern pioneer. In 2019, the then Mayor Claudia Sheinbaum (now, of course, President Sheinbaum) launched the Cosecha de Lluvia (Rain Harvest) programme to install domestic systems across the city. I wrote in my book, “From 2019 to 2021 they installed 31,239 harvesters, benefiting almost 150,000 people directly.” By 2024, this had grown to 73,000 systems installed. For communities without mains water, rain capture has meant autonomy, saved time, and cleaner homes.
As Mexico Business News reports, “65% are in homes led by women, who traditionally have been responsible for securing water for their families. The program allows these women to redirect their time to other activities, improving their quality of life.”
Even greater savings can be made when these systems are combined with smart appliances that use far less water to begin with. One UK-based project saw over a hundred Propelair low-flush toilets installed on the Exeter University campus. Using an air tank as well as a water tank and an air-tight toilet lid – working in a similar way to an aeroplane toilet – the Propelair uses just 1.5 litres of water per flush, compared to the 7–10 litres of a conventional toilet. This was combined with a large rainwater capture tank, meaning the entire campus building’s toilet block runs in effect without using mains water.
On a recent trip to Ikea (something I’ve managed to reduce to about a once-a-decade ordeal) I was also pleased to see the following signage in the customer toilets (see pic below). It was a guilt-free flush. The concept of flushing toilets with expensively treated drinking-quality water needs to (and will do, I predict, in our lifetime) become a social anathema.
Sign inside IKEA store
It’s also worth remembering that there’s nothing truly new or modern about any of this. Long before desalination plants and smart toilets, entire civilizations relied on harvested rainwater. The sixth-century Byzantines built the astonishing Basilica Cistern beneath Constantinople – an underground cathedral of 336 columns that stored 800 million litres of water, enough to withstand a siege. Even older, the Nabataeans of Petra (one of the ‘Seven Wonders of the World’, in modern-day Jordan) carved a pressurised water systems into the rock itself, with aqueducts, dams and cisterns that protected the city from flash floods and kept 20,000 people supplied for months.
One of my favourite facts gleaned from my visit there was of a piece of papyrus restored in 1995 which recorded a legal dispute between two Nabatean neighbours over the water spout on their connected roofs: Stephanos had built an extension which took more of the water, and Theodoros did not approve. Rainwater was well worth suing your neighbour over.
Bronze Age engineers in Jawa, near today’s Syrian border, built one of the world’s first water-harvesting systems 5,000 years ago – stone-lined canals and deflection dams capturing the winter rain. Carved onto the famous Mesha Stele, a polished black block of basalt about a metre tall, dated to around 840 BC, King Mesha of Moab is recorded to have commanded his citizens: “Make yourselves each a cistern in his house.”
Modern civilization’s dependence on centralised, energy-hungry water infrastructure looks brittle compared to the resilience of ancient systems. Many of them – like Petra’s flood defences or Iran’s qanats – still function today. Qanats, a network of underground tunnels stretching for thousands of kilometres across Iran and Central Asia, once supplied whole communities through gravity-fed channels that also recharged aquifers. They are in effect rainwater harvesting and managed-aquifer-recharge (MAR) combined. As I wrote in my book, “Iran has over 36,000 qanats – if you lined them up end to end, they would go round the equator nine times.” UNESCO now recognises the qanats as a World Heritage system, and some are being revived as Iran faces amongst the most acute water crisis in the world. In the Peruvian Andes, farmers are also reviving qochas – high-altitude rain ponds that recharge the soil and springs.
The lesson, as I wrote in The Last Drop, is simple: “Multiple, decentralised systems are often more sustainable than the mega projects of today.”
Modern technology can help – smart sensors, low-flush toilets, precision irrigation – but the principle is ancient. Capture the rain where it falls. Use it wisely. Respect water as a shared resource, not a commodity to be bought and wasted.
Rajasthan, India, Om Prakash Sharma of the Anglo-Indian water charity WaterHarvest told me, is “literally destroying 5,000 years of water wisdom in the whole region within thirty to forty years.” He’s right – but he’s also leading the fight to turn this around. To date, WaterHarvest has directly supported over two million people, worked in over 2,000 villages, and built structures to harvest 1.68 billion litres of rainwater annually. And as of 2024, are now working in Africa too – having built 107 rainwater harvesting tanks at 22 schools in Uganda.
Meanwhile in Iran, on the 3rd of May this year, the Tehran Times reported of a traditional ceremony of casting flowers and rosewater on the flowing waters of qanats was held in Bam, southern Iran:
“The event coincided with the National Day of Qanats in Iran… marked the symbolic beginning of the annual maintenance work in the qanats. In the past, local well diggers, known as moqannis, would enter the aqueducts after performing ablution, carrying flowers and sprinkling rosewater in honor of the precious water sources. This act not only signified reverence for nature but also expressed gratitude for the ingenuity of ancestors who developed this vital water system.”
The practice is described as having “faded from memory for over half a century” but is now “officially revived”.
In the UK, too, the multiple uses of rainwater have been forgotten. It clings on in many regions as the humble garden water butt; its use reduced to merely watering some plants. But as the drought of 2025 shows, we need to relearn and revive its use for much more besides. The bad news of modern water systems and climate change, is that water has become both more scarce and more expensive than ever before. The good news is: the solution literally falls from the sky.
