Between two and three billion people worldwide experience water shortages, according to a 2023 report by UNESCO and UNWater. And these shortages are set to worsen in the coming decades, especially in cities, the organizations warned.
On a country-specific basis, the PBL Netherlands Environmental Assessment Agency recently estimated water shortages to be an important climate-change related risk in the Netherlands. Meanwhile, “all-or-nothing” rainfalls have also been causing water scarcities throughout England.
As climate-change is expected to ramp up, rainwater harvesting, using modern pumping technology, could be needed to alleviate drought. Steven Walker, technical sales manager at pump manufacturer Wilo UK, explains more, “Rainwater harvesting is becoming ever more critical. Water shortages, hose pipe bans, and unpredictable rainfall patterns are all news items that have become all too familiar in recent years. With these trends likely to continue, it’s clear that we need to harness rainwater as a sustainable option,” Walker adds.
In the UK, Wilo is calling for developers and consultants to install rainwater harvesting systems in new buildings and commercial developments to help with potential future water shortages (see An opportunity for rainwater harvesting pump systems, below). One country ahead of the game in this area is Australia. World Pumps got advice from experts at Melbourne’s Swinburne University of Technology which has carried out extensive research into the use of rainwater harvesting and the roles pumps can play.
“In Australia, we had the millennium drought,” says Magnus Moglia, associate professor at Swinburne University of Technology, researching sustainability solutions. It started with low rainfall in late 1996 and went on through 1997. It intensified in 2001 and 2002, and by 2003 it was recognized as the worst drought on record. The emergence of La Niña weather conditions in 2010 rapidly ended the drought, and led to floods in some locations, particularly in central and southern Queensland.
This drought caused rainwater harvesting to become ingrained in Australian living, partly due to government mandates and incentives, and partly because of water shortages and restrictions. “People weren’t allowed to water their garden with mains water,” Moglia explains. “And outside the cities, where it’s impossible to connect to the mains, lots of people are fully relying on rainwater.”
Drought and flood resilience
In 2016, Moglia worked with other researchers to publish a report on the “Investigation of pump and pump switch failures in rainwater harvesting systems,” because CSIRO, Australia’s federal research agency, wanted to understand their quality. “That coincided with interest from water companies in storm and rainwater,” Moglia comments. “Because urbanization in cities like Melbourne and Sydney is taking over more land, there was a need for more rainwater tanks to maintain waterways.”
In Melbourne, 31% of households now harvest rainwater. “The most value for the city is in reducing urban flooding and damage to waterways. If people have nearly empty rainwater tanks, they can capture as much as possible. So, there are recommendations in some places that if there’s large rainfall coming, you empty your rainwater tanks beforehand,” he adds.
The rainwater systems
“Rainwater tanks have been used since ancient times and you can make them as easy and complicated as you like,” Moglia says. Stage one is connecting a large container to the drainpipe of your house and using it to water the garden or wash the car: convenient, cheap and no pumps required. But this will save a household on average only 12m3/yr of mains water.
If rainwater is also used indoors, i.e. for the toilet and the washing machine, an extra 34m3/yr can be saved. This requires a more involved system, costing a few thousand dollars. “There is the cost of the pump,” Moglia explains. “It requires plumbing. You must buy the actual tank: 5m3 is not unusual. And you have to make sure the foundation is sound.”
The pump typically consumes 1.8 kWh/m3. “There are a few tricks to reduce pump energy consumption,” Moglia says. “The problem is that the pump goes on many times for just a short amount of time.” It’s more efficient to pump the water from the main tank up to a buffer of 100 to 200 liters in the attic or on the roof. Then gravity can feed the toilet and washing machine, and the pump doesn’t have to turn on and off so often. Also, it’s essential to choose the right pump size: “If it’s significantly over-dimensioned,” Moglia explains, “it can be outside its efficient area of operation.” A switch is also required to change to mains water if the rainwater tank is dry. This can be manual or automatic, triggered by a float.
Screens are needed to block mosquitoes. And extras can be added like a flush diverter. This discards the first water of every rainfall, so that the brown, tannin-like muck gathering on the roof from bird droppings and rotting leaves during dry spells doesn’t get into the tank.
Teething problems
Although these systems seem low-tech, in the real world, many turned out to be faulty. The foundations of rainwater tanks were frequently found inadequate: 13% were even leaning against a structure. “It’s a lot of weight,” Moglia says. “You don’t want that leaning up against a wall.”
Pump failures were found in 5% of the systems: more often (14%) in builder-installed than in plumber-installed (3%) systems. Anecdotal evidence suggests that checks after installation may not have been as stringent in builder-installed systems.
A quarter of all inspected sites had an automatic switch of which about a third was faulty. “We often found them broken and people didn’t realize,” Moglia comments. “So, they weren’t actually using rainwater.”
In manual switches no faults were found. “There’s a benefit in simple design,” Moglia says. “If you go out regularly to turn on the pump yourself, you’ll quickly realize if there are problems, like smelly water.” Regularly checking the pumps and switches is estimated to cut problems in half. “So, every few months, check your pump is making the right noises, actually putting pressure on and checking it’s not leaking,” Moglia says. “Often the pump is out in the weather, so it’s worthwhile to cover it up.”
In about a quarter of the tanks, mosquitoes had found their way in. The most common access routes were the tank inlet and overflow. So, all potential access routes have to be thoroughly sealed. In systems with adequate protection, mosquitoes were still found in 4% of cases. Therefore, it requires regular checking and maintenance. “We found storm water overflows to be a challenge,” Moglia explains. “Many people look at the inlets. But the overflow seems to be a blind spot.”
Drink at your own risk
Lastly, 57% of tanks had discolored water, 19% had smelly water, and 6% had high sediment concentrations. “If you want to avoid brown water, which is mostly organic matter decomposing in the gutters, you install netting that prevents leaves getting into the gutters,” Moglia says. “And secondly you clean them. But it’s inevitable you’ll have some fecal contamination from birds, and in Australia possums and even mice and snakes.”
Still, it’s quite common for people to add a filter and UV sterilization and drink their rainwater. “In a study in Brisbane they found pretty much all rainwater tanks had some sort of contamination,” Moglia says. “But according to epidemiological studies, it’s not really an issue for people who drink it. So, it’s relatively safe to drink but personally, I prefer to drink mains water.”
If there is lead flashing on the roof, it must be removed, since lead-contaminated water is unsuitable for drinking or plant watering. The quality of rainwater can also be compromised in places with substantial air pollution, Vietnam for example. “In the places we studied,” Moglia says, “air quality was good.”
Let’s get this right
Rainwater harvesting is not just for outbackers anymore: we might need it in the future. Although it’s well-proven technology, we’re using it in new ways, and modern consumers have high standards. The teething problems found in Australia have to be avoided, especially if we’re offering this technology to first-adopters.
“These are the most prescient people,” Moglia elaborates. “They put their money, time and effort into it. If it doesn’t work as they hoped, you’ll lose their support.” Fortunately, we can learn from the Australians, and, as Moglia adds, others as well: “Rainwater tanks have been used in many places, like India and China. They’re all a bit different.”
Earlier this year, pump manufacturer Wilo UK issued a call to action for developers and consultants in the UK to install more rainwater harvesting systems in new builds and commercial developments to help with potential future water shortages and reduce eliance on potable water.
The callout followed news from the UK Government that there will be a predicted deficit of almost five billion liters of water a day by 2050, more than a third of the water currently put into public supply.
Wilo highlighted that rainwater harvesting systems that collect and pump rainwater around buildings, while not mandated, can significantly lower water bills while improving a building’s green credentials in a time where sustainability and costs are of high priority. The rainwater, for example, can be used for flushing toilets in offices and student accommodation.
The pump manufacturer also flags that rainwater harvesting systems are not as complicated as some may believe, with systems often only requiring a few pieces of equipment. This includes a rainwater storage tank, a rainwater pump, and low-maintenance filtering and cleansing solutions distributing water at a suitable pressure to specific outlets throughout a building.
Steven Walker, technical sales manager at Wilo UK, said, “With the National Drought Group recently reiterating the importance of planning and investing for all weather events, we must look beyond potable water supply and consider the opportunity presented by rainwater harvesting systems. Such solutions crucially help to increase the green credentials of any building, and the developer, contributing to a better BREEAM score through efficient water consumption.”
The latest innovative rainwater harvesting pumps include the ability to automatically replenish tanks with potable water, if the external storage tank is running low following insufficient rainfall, ensuring sufficient supply whatever the weather. Alongside this, optional controls and a simple-to-understand touchscreen means building managers can monitor and adjust the pump easily, according to the needs of the occupants in the building.
About the author
This article was written by Django Mathijsen, a freelance writer
This article first appeared in the July/August 2024 issue of World Pumps magazine. To read the full issue, click here.
