Quantcast
Environmental News for a Healthier Planet and Life

Help Support EcoWatch

Roof-to-Garden: How to Irrigate with Rainwater

Popular
Kodachrome25 / Getty Images

By Brian Barth

The average American household uses about 320 gallons of water per day, a third for irrigation and other outdoor uses. Collecting the water flowing down your downspouts in rainstorms so you can use it to irrigate in dry periods is often touted as a simple way to cut back. But setting up a functional rainwater irrigation system—beyond the ubiquitous 55-gallon barrels under the downspout, which won't irrigate much more than a flower bed or two—is a fairly complicated DIY project.


If you live in a townhouse or apartment with a tiny yard, one of those store-bought barrels will probably do the trick. In that case, there's not much to know—most come with instructions and all the hardware you need. But if you're planning a more ambitious project consider the following pointers before getting started. Before you begin, make sure that rain harvesting is legal in your area.

Calculating Your Water Budget

To give you an idea of how much water you have at your disposal for irrigation, here is a simple equation for figuring out how many gallons your roof sheds when it rains:

roof size (in square feet) X annual rainfall (in inches) X .6

There are rain tank calculators online so you don't have to do the math, but here is an example. If you lived in a modest 20' by 30' house (measure roof size as the length times the width of the house) in a modestly wet region with 40 inches of annual rainfall, that's (20 X 30) X 40 X .6 = 14,400 gallons. Here's a handy web tool to find out how much rainfall you get in your area each year.

In a very dry climate where most of the rain falls in winter, as is the case along most of the West Coast, you could easily use that much irrigation water in spring, summer, and fall—and much more, depending on the size of your garden. But if you live an area that typically gets rainfall throughout the warm parts of the year (plants rarely need irrigation in the winter), how much water you can catch in a year is not as relevant as how much you'll need during a summer dry spell.

Irrigation needs vary considerably depending on climate, shade, soil type, and vegetation type, but this equation will give you a rough idea of your garden's water demand:

area to be irrigated (in square feet) X maximum number of weeks between major summer rainstorms X .5

If you have a modest 30' by 30' yard and want to have enough water to irrigate for a month-long dry spell (light rain doesn't count—at least one inch of precipitation is needed to saturate the soil in dry conditions), which is not uncommon in most of the country (except in the Southwest and on the West Coast, where dry spells last many months), that's (30 X 30) X 4 X .5 = 1800 gallons.

In arid regions like Los Angeles or Phoenix, where eight months can pass between major rainstorms, the equation looks like this (30 X 30) X 32 X .5 = 14,400 gallons. So you can see why it makes sense to focus on how much you can actually collect from your roof in such climates, rather than how much you can use.

Sizing the System

The size of your rainwater catchment system may ultimately depend on your budget and how much space you are willing to dedicate to it. Rainwater is typically stored in polyethylene (plastic) tanks, which can be purchased at farm supply stores or shipped from online suppliers like The Tank Depot and Plastic-Mart. Most tanks cost roughly 50 cents per gallon of storage, though the larger sizes are often much pricier.

Larger tanks are also very unwieldy to install and are an eyesore in the landscape. A 15,000-gallon tank, for example, is roughly 12 feet in diameter by 18 feet tall and weighs more than 3000 pounds. Most people who want to store that much water opt for three 5000-gallon tanks, which are roughly 10 feet in diameter by 10 feet tall and weigh 800 pounds—light enough for a few strong people to push around and maneuver into place. Most folks in urban areas prefer to stick with 1000-gallon size tanks (6 feet in diameter by 6 feet tall and around 200 pounds), or smaller.

Finding a Location

Tanks are typically positioned at or near a downspout so the water can be funneled in directly. Rain tanks aren't pretty, so you'll probably want to situate them out of sight, or conceal them with a trellis, shrubbery, or other enclosure.

One option to prevent an eyesore next to your house is to collect water in small barrels at the downspouts, and then pump the water into a large central tank located away from the house. Another option is to bury rain tanks near the house—in this case, they'd be considered cisterns—and let the water flow from the downspouts through buried drain pipes and into the tanks. Typical polyethylene tanks may not be used underground, though specially designed underground tanks are available (they cost two to three times as much as aboveground tanks, however).

Of course, you can also collect water from the roofs of barns, sheds, and other outbuildings, which may offer better opportunities to conceal the tank than positioning it next to your house. Keep in mind that each downspout only drains a portion of the roof, so match tank size to roof area accordingly. Where you have several downspouts along one side of a house or outbuilding, it's possible to combine the flows into a single tank.

Installation Basics

Rain tanks are extremely heavy when full of water (water weighs about 8 pounds per gallon), so you need to create a firm base for them to rest on; otherwise, the earth below may settle under the weight and cause the tank to shift.

First, remove the topsoil and then spread a 6-inch layer of gravel or granite fines to create a pad for the tank, grading the surface flat and smooth and tamping it (with a manual tamper for small areas, or a power tamper for large installations) to prevent the material from settling. Building codes typically require a 6-inch concrete slab to be poured as a base for tanks 5000 gallons in size and larger.

Next, you'll need to route the downspouts to the openings on top of their respective tanks. Simply cut into existing downspouts above the height of the tank and use a combination of "A" and "B" style elbows and lengths of downspout (a selection of gutter supplies is available at any building supply center) to reroute the downspout to the tank. Use a carpenter's level to ensure that horizontal sections of downspout are sloped "downstream" at a minimum ratio of ¼-inch per linear foot.

Here are a few recommended accessories to place between the top of the downspout and the opening of the tank:

  • A tank screen to prevent smaller gutter debris from washing into the tank, and to keep mosquitoes and rodents out of the tank.
  • A first flush diverter to divert the first bit of water from each rainfall, which may contain bacteria from dead insects, lizards, rodents, snakes and other critters that sometimes end up in gutters, as well as bird and animal droppings, chemical residues and fine particles from roofing materials, and anything else that might wash of your roof that an irrigation system is better off without.

All rain tanks have an overflow outlet near the top of the tank that should be connected by drain pipe to the drainage system that the downspout previously flowed into.

Connecting to the Irrigation System

Your irrigation system may be as simple as a hose connected to the valve at the bottom of the rain tank. Of course, this gravity-powered approach only works if the area you're irrigating is lower in elevation than the water level inside the tank.

Sprinklers and drip irrigation systems are likely to require a pump to provide sufficient water pressure unless the tank is significantly higher in elevation than the area to be irrigated. Each foot of elevation results in .43 pounds per square inch (psi) of water pressure. Drip systems generally require at least 15 psi (35 feet of elevation), while most sprinkler systems require at least 30 psi (70 feet of elevation).

There are a variety of pumps and pump accessories available to pressurize your irrigation system with water from a rain tank, but unless you have serious plumbing and electrical expertise, you're better off hiring an expert for this part. Setting up an effective pumping system depends on the specific context of your water storage and irrigation system; there are many technical details to be aware of to make sure you get the pressure you need, minimize electricity consumption, and avoid wearing out your (expensive) pumping equipment prematurely.

For automated irrigation systems, it's possible to tie the pump to the irrigation control box, so when each irrigation valve opens according to its schedule, the pump kicks on and provides water from the tank.

Reposted with permission from our media associate Modern Farmer.

EcoWatch Daily Newsletter

Cyclists ride through an intersection in downtown Brooklyn on July 30, 2019 in New York City. Drew Angerer / Getty Images

Mayors from some of the world's major cities have unveiled their vision for how the world can recover from the coronavirus pandemic while encouraging environmental justice and fighting the climate crisis.

Read More Show Less
A woman wears a face mask at a Walmart store in Washington, DC on July 15, 2020. ANDREW CABALLERO-REYNOLDS / AFP via Getty Images

Walmart, the world's largest retailer, will start requiring next week that all its stores in the U.S. deny entry to any customer not wearing a mask, as CNN reported. The announcement comes after months of a pandemic that has led to more than 3.5 million coronavirus cases and more than 130,000 deaths nationwide.

Read More Show Less
Agencies in California, Washington and British Columbia are sharing data and strategies to protect forests from wildfires. Joe Mabel / Wikimedia Commons / CC by 4.0

Some of the largest wildfires on record have swept across the West in recent years.

Read More Show Less
Start-up ARC Marine has created a plastic-free alternative to help restore marine biodiversity. ARC Marine

By Douglas Broom

Artificial reefs play an important role in protecting offshore installations like wind farms. Unprotected, the turbine masts are exposed to tidal scouring, undermining their foundations.

Read More Show Less
New research shows that there's actually a larger quantity of plastic in the ocean than previously thought. Susan White / USFWS / Flickr / CC by 2.0

By Elizabeth Claire Alberts

In 1997, Charles Moore was sailing a catamaran from Hawaii to California when he and his crew got stuck in windless waters in the North Pacific Ocean. As they motored along, searching for a breeze to fill their sails, Moore noticed that the ocean was speckled with "odd bits and flakes," as he describes it in his book, Plastic Ocean. It was plastic: drinking bottles, fishing nets, and countless pieces of broken-down objects.

"It wasn't an eureka moment … I didn't come across a mountain of trash," Moore told Mongabay. "But there was this feeling of unease that this material had got [as] far from human civilization as it possibly could."

Captain Charles Moore looking at a piece of floating plastic in the ocean. Algalita Marine Research and Education

Moore, credited as the person who discovered what's now known as the Great Pacific Garbage Patch, returned to the same spot two years later on a citizen science mission. When he and his crew collected water samples, they found that, along with larger "macroplastics," the seawater was swirling with tiny plastic particles: microplastics, which are defined as anything smaller than 5 millimeters but bigger than 1 micron, which is 1/1000th of a millimeter. Microplastics can form when larger pieces of plastics break down into small particles, or when tiny, microscopic fibers detach from polyester clothing or synthetic fishing gear. Other microplastics are deliberately manufactured, such as the tiny plastic beads in exfoliating cleaners.

"That's when we really had the eureka moment," Moore said. "When we pulled in that first trawl, which was outside of what we thought was going to be the center [of the gyre], and found it was full of plastic. Then we realized, 'Wow, this is a serious situation.'"

Captain Charles Moore holding up a jar of plastic-filled seawater from a research expedition in 2009. Algalita Marine Research and Education

Since Moore's discovery of the plastic-swirling gyres, there's been a growing amount of research to try and understand the scale of the plastic pollution issue, including several studies from 2020. This new research shows that there's actually a larger quantity of plastic in the ocean than previously thought, and that the plastic even enters the atmosphere and blows back onto land with the sea breeze. Recent studies also indicate that plastic is infiltrating our bodies through food and drinking water. The upshot is that plastic is ubiquitous in the ocean, air, food supply, and even in our own bodies. The new picture that is emerging, scientists say, is of a biosphere permeated with plastic particles right down to the very tissues of humans and other living things, with consequences both known and unknown for the lifeforms on our planet.

How Much Is Really in the Ocean?

In the past 70 years, virgin plastic production has increased 200-fold, and has grown at a rate of 4% each year since 2000, according to a 2017 study in Science Advances. Only a small portion of plastics are recycled, and about a third of all plastic waste ends up in nature, another study suggests.

While new research indicates that plastic is leaking into every part of the natural world, the ocean has long been a focal point of the plastic pollution issue. But how much is actually in the sea?

Moore says it's "virtually impossible" to get an accurate estimate because of the ongoing production of plastic, and the tendency for plastic to break down into microplastics.

"This count is constantly increasing, and it's increasing at a very rapid rate," he said. "It's a moving target."

One commonly cited study, for which Moore acted as a co-author, estimated that there are more than 5.25 trillion plastic pieces floating in the ocean, weighing more than 250,000 tons, based on water samples and visual surveys conducted on 24 expeditions in five subtropical gyres. But even at the time of publication in 2014, Moore said he knew "that was an underestimate."

A more recent study published this year, led by researchers at Plymouth Marine Laboratory, indicates that there's a lot more microplastic in the ocean than we previously thought. When taking samples from the ocean, most researchers use nets with a mesh size of 333 microns, which is small enough to catch microplastics, but big enough to avoid clogging. But the team from Plymouth Marine Laboratory used much finer 100-micron nets to sample the surface waters in the Gulf of Mexico and the English Channel.

"Our nets clogged too, so we used shorter trawls and a specialized technique for removing all the plankton — microscopic plants and biota — from the sample to reveal the microplastics," Matthew Cole, a marine ecologist at Plymouth Marine Laboratory and author of the study, told Mongabay in an email. "This process is quite time-consuming, so it'd be challenging for all samples collected to be treated this way."

The research team at Plymouth Marine Laboratory collecting water samples. Matthew Cole

The researchers found there were 2.5 to 10 times more microplastics in their samples compared to samples that used 333-micron nets.

"If this relationship held true throughout the global ocean, we can multiply existing global microplastic concentrations ascertained using 333-micron nets, to predict that globally there are 125 trillion plastics floating in the ocean," Cole said. "However, we know these plastics keep on degrading, and these smaller plastics would be missed by our smaller 100 micron net — so the true number will be far greater."

Another team of researchers delved down to the seafloor in the Tyrrhenian Sea in the Mediterranean to take sediment samples. They found that microplastic accumulated at depths of 600 to 900 meters (about 2,000 to 3,000 feet), and that certain spots in the ocean, termed "microplastic hotspots," could hold up to 1.9 million pieces per square meter — the highest level ever to be recorded on the seafloor. The results of this study were published in Science in June 2020.

"We were shocked by the sheer number of [microplastics]," Ian Kane, the study's lead author, told Mongabay in May. "1.9 million is enormous. Previous studies have documented much smaller numbers, and … just talked about plastic fragments, but it's fibers that are really the more insidious of the microplastics. These are the things that are more readily consumed and absorbed into organisms' flesh."

A water sample containing plastic. Algalita Marine Research and Education

While these studies shine light on the fact that there's definitely more plastic in the ocean than we think, it still doesn't complete the picture, says Steve Allen, a microplastic expert and doctoral candidate at the University of Strathclyde in the U.K. Large quantities of microplastics still appear to be "missing" from the ocean, he said. For instance, one study suggested that 99.8% of oceanic plastic sinks below the ocean surface layer, making it difficult to detect, but Allen says this doesn't fully explain what's happening to all of the plastic that enters the ocean.

"We're finding some of it," Allen told Mongabay. "But we're … trying to explain where the rest of it went."

Allen and his wife, fellow scientist Deonie Allen, also from the University of Strathclyde, have been working to find their answer, or at least part of it, in an unlikely place: up in the sky.

‘Microplastics Are in Our Air’

As the ocean churns and breaks waves, air is trapped in tiny bubbles. When those bubbles break at the sea's surface, water rushes to fill the void, and this causes tiny, micro-sized particles, like flecks of sea salt or bacteria, to burst into the atmosphere. A new study, published in PLOS ONE, suggests that microplastics are entering the air in the same way.

"[Bubbles] act a little bit like velcro," Deonie Allen told Mongabay. "Rather than the bubble going through the plastic soup and coming to the surface and not bringing any of the plastics with it, it actually collects [the plastic] and hangs on to it as it comes up. And when it bursts, the energy from the creation of the jet to fill the hole that's left in the sea … is what gives it the force to eject the plastic up into the atmosphere."

A lot of previous research on plastic pollution in the ocean has assumed that plastic remains in the seawater and sediment, or gets washed ashore. But this study takes a pioneering step to suggest that ocean plastic is entering the atmosphere through the sea breeze.

"This was just the next logical step to see whether what we're putting into the ocean was actually going to stay there, or whether it would come back," Steve Allen said.

A device used to collect air and mist samples to test for microplastics. Steve Allen

To obtain the necessary data for this study, the research team collected air and sea spray samples on the French Atlantic coast, both onshore and offshore. They found that there was a high potential for ocean microplastics to be released into the air, and suggested that each year, 136,000 tons of microplastics were blowing ashore across the world, although Steve Allen said this number was "extremely conservative."

This study specifically looked at microplastics, but the much smaller nanoplastics are likely going into air by the same means, according to the Allens. But detecting nanoplastics in the water or air can be challenging.

While this is the first study to look at the ocean as a source of atmospheric plastics, other research has examined the capacity of land-based plastics to leach into the air. One study, authored by the Allens and other researchers, found that microplastics were present in the air in the Pyrenees Mountains between France and Spain, even though the testing site was at least 90 kilometers (56 miles) from any land-based source of plastic, such as a landfill. This suggests that the wind can carry microplastics over long distances.

"We know that microplastics are in our air everywhere, from the looks of it," Deonie Allen said.

More research needs to be done to understand the implications of atmospheric microplastics on human health, but according to the Allens, it can't be good for us.

A "cloud catcher" used to collect data for research on microplastics in the atmosphere. Steve Allen

"Microplastics are really good at picking up the contaminants in the surrounding environment — phthalates, flame retardants, heavy metals," Deonie Allen said. "That will get released into the body, relatively effectively."

Enrique Ortiz, a Washington, D.C.-based ecologist and journalist who writes on the plastic pollution issue, says that this evidence should be a "wake up" call to humanity.

"The oceans are picking up the plastic that we throw in it, and that's what we're breathing," Ortiz told Mongabay "And that's the part that really … amazes me."

"But it's not just happening in coastal cities," he added. "No matter where you go, [even] in the middle of the Arctic … the human imprint is already there."

We're not just inhaling microplastics through the air we breathe — we're also getting it through the water we drink and the food we eat.

‘Our Life Is Plasticized’

Plastic waste isn't just leaking into the ocean; it's also polluting freshwater systems and even raining or snowing down from the sky after getting absorbed into the atmosphere, according to another study led by Steve and Deonie Allen. With microplastics being so ubiquitous, it should come as no surprise that they are also present in the food and water we drink.

Drinking water, including tap and bottled water, is the largest source of plastic in our diet, with the average person consuming about 1,769 tiny microplastic particles each week, according to a 2019 report supported by WWF. Other primary sources of microplastics include shellfish, beer and salt.

A new study published this year in Environmental Research found that microplastics were even present in common fruits and vegetables. Apples had one of the highest microplastic counts, with an average of 195,500 plastic particles per gram, while broccoli and carrots averaged more than 100,000 particles per gram.

"The possibility of plastics in our fruit and vegetables is extremely alarming," John Hocevar, ocean campaign director for Greenpeace USA, said in a statement. "This should prompt additional studies to assess how much plastic we are consuming through our produce each day and examine how it is impacting our health."

"Decades of plastic use have contaminated our air, water, and soil," Hocevar added. "Eating just a bite of an apple could now mean eating hundreds of thousands of bits of plastic at the same time."

Through normal water and food consumption, it's estimated that the average person consumes about 5 grams of plastic each week, equivalent to the size of a credit card, according to the WWF report.

"Plastic is everywhere," Thava Palanisami, a microplastics researcher at the University of Newcastle, Australia, and contributor to the WWF report, told Mongabay. "We live with plastic and our life is plasticized — that we know. But we don't know what it does to human health. That's the biggest question mark."

While it's not entirely clear how plastic affects human health, research suggests that the inhalation of fibrous microplastics can lead to respiratory tract inflammation. And another study, referenced in the WWF report, shows that fish and other marine animals with high concentrations of microplastics in their respiratory and digestive tracts have much higher mortality rates. Another study, published in 2020, indicates that plastic accumulates in the muscle tissue of fish.

"If you look at what happens, for example, in fish — it [plastic] stays in their muscles," Ortiz said. "It's scary. If you look at the numbers, you're eating something in the order of one kilo of plastic every three years. I wonder, in our lifetime … if a percentage of our weight will be plastic that is still in our muscles."

"The problem is serious," Palanisami said. "We've got to stop using unwanted plastic and manage plastic waste properly, and … work on new plastic alternates."

Stemming the Tide  

Erin Simon, head of plastic waste and business at WWF, and leader of the organization's packaging and material science program, says the key to curbing the plastic pollution issue is making sure that plastic doesn't leak into nature in the first place.

"If you had a leaky faucet, would you bring out the mop first, or would you turn off the water?" Simon told Mongabay. "We're trying to stem that tide of plastic flowing into the ocean and into nature in general … but at the same time, trying to identify the different root causes of that leakage."

While Simon says there are various ways to try and stop plastic from entering the natural world, such as well-managed recycling and composting programs, she also said that large companies can play a critical role in helping to reduce plastic waste. WWF is currently spearheading a new program called ReSource, launched in 2019, that helps analyze companies' plastic footprints in order to work toward sustainable solutions. The program's website says 100 companies could prevent 50 million tons of plastic waste.

"We have three targets that we're looking at when we're partnering with companies," Simon said. "One, get rid of what you don't need. At the end of the day, we do need to reduce our demand for virgin nonrenewable plastic. Once you get rid of that, you think about the stuff that you do need — the things [for which] plastic is the right material choice. Where am I sourcing that from? Am I getting it from recycled content? Am I getting it from a sustainably-sourced bio base, or is it virgin non-renewable [plastic]? And then finally … how are you, as a company … making sure it comes back? Are you designing it in a way that it's technically recyclable into the places that it's ending up?"

Marine debris litters a beach on Laysan Island in the Hawaiian Islands National Wildlife Refuge, where it washed ashore. Susan White / USFWS

While recycled plastic may seem like a satisfactory alternative to virgin plastic, a new study, published in July 2020, showed that children's toys made out of recycled plastic contained high levels of toxic chemicals, comparable to levels found in hazardous waste.

Moore, who has been studying plastic pollution since his discovery of the floating debris in the North Pacific Ocean, says he doesn't believe there's an easy fix to this issue, especially when it comes to the businesses that are producing large amounts of plastic.

"There's no change that corporations can make under the current system that will successfully combat plastic pollution," Moore said. "There is no technical fix to the plastic problem. It's not in the corporate portfolio to reduce sales of your products — the corporate portfolio is about increasing sales. The idea that [corporations] can be convinced to reduce their production and sale of the products that they make is a fantasy."

However, Moore says a solution could be found in "radical change," and that this moment of time, with the Black Lives Matter movement spreading across the world, could provide the opportunity for that change.

"Now is the time when a world historical revolution would be possible, when the people of the world could unite to change the system as a whole," Moore said.

"There won't be a techno fix and science won't develop … a new product that will get us out of the problem of plastic pollution," he said. "It will only come with the world as a whole agreeing to charter a new course towards a non-polluting future."

Reposted with permission from Mongabay.

Scientists say that a record-breaking Arctic heat wave was made 600 times more likely by the man-made climate crisis. PBS NewsHour / YouTube

The record-breaking heat in the Arctic saw temperatures soar above 100 degrees for the first time in recorded history. Now, a new analysis has put to rest any notion that the heat was caused by natural temperature fluctuations.

Read More Show Less

Trending

Commuters arrive at Grand Central Station with Metro-North during morning rush hour on June 8, 2020 in New York City. Angela Weiss / AFP / Getty Images

By Taison Bell

"Hospital Capacity Crosses Tipping Point in U.S. Coronavirus Hot Spots" – Wall Street Journal

This is a headline I hoped to not see again after the number of coronavirus infections had finally started to decline in the Northeast and Pacific Northwest. However, the pandemic has now shifted to the South and the West – with Arizona, Florida, California and Texas as hot spots.

Read More Show Less