July 17, 2019
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How to harvest rainwater

Photo by Roslynn Brain McCann | Roslynn Brain McCann
Photo by Roslynn Brain McCann | Roslynn Brain McCann
Rain tank at the Santa Fe Children's Museum.

No matter if you live in the rainy Pacific Northwest or the bone-dry Southwest, your land enjoys the occasional refreshing rainstorm. Instead of letting this rainwater wash away, harvest and utilize it in your garden or home.

“We’re experiencing a warming climate, and water scarcity is becoming an increasing reality,” said Roslynn Brain McCann, sustainable communities extension specialist at Utah State University Moab. “We’re moving away from relying on municipal water.”

Harvesting rainwater can not only help you save water and spend less on your bills, but it can also help you better manage the ecosystem of your property.

“If you do it in an integrated manner, not only is it very high-quality, free water source, but it will also help you reduce onsight flooding,” said Brad Lancaster, author of “Rainwater Harvesting for Drylands and Beyond.”

Harvesting rainwater can also be beneficial for local ecosystems.

“When you have a big stormwater surge after a rain event, it’s all going out into the street at the same time,” McCann explained. “That carries debris [and] pollutants [that] stress local waterways.”

Using rainwater in lieu of municipal water also eases the stress that municipal water systems exact on local aquatic ecosystems.

“We’re keeping more of that water in the places that it needs to be,” McCann added. “This also relates to reducing the need to withdraw water from lakes and streams. The less that we are pulling from other systems, ideally the more water will remain in them.”

What can you do with rainwater?

Lancaster said you can basically use rainwater to do anything you do with other water: cooking, washing, flushing toilets and everything in between.

Harvested rainwater is especially good for irrigating gardens or outdoor landscaping. Lancaster said that in the West, groundwater and surface water tends to be really high in salt which is problematic for plants. Rainwater also contains natural fertilizer in the form of nitrogen fixed by atmospheric forces like lightning.

You can also harvest and store rainwater in cases when drought or other emergencies compromise your access to municipal water supplies and electricity.

“You can set it up so that it can be a water source that’s available even when the power goes out,” Lancaster said. “It’s very easy to make it a gravity-fed system [that does not require power].”

Is it legal to collect rainwater?

The rules governing rainwater collection depend on where you live.

“Different states have different policies,” McCann said. “In Utah, many people think it’s still illegal because it had been for quite a while.”

Some states, like Kansas, require permits for rainwater collection in general, while others have specific limitations or restrictions — for example, on the size of rain barrels.

“The state of Utah allows for 2,500 gallons in an above or underground tank. It could be in many tanks, but it cannot total more than 2,500 gallons without a special permit,” McCann said. “Mine is 1,500 gallons, and I’m not even using the full potential of my house.”

In order to find out where the regulations are where you live, contact your local government.

“You can call your local building inspector,” Lancaster said. “Sometimes, it might be your Department of Environmental Quality, but I would start with the building department.”

Can you drink rainwater?

You can drink rainwater as long as it is properly filtered before you consume it.

“If you’re going to drink it or cook with it, just play it safe and filter it before you do so,” Lancaster said.

The filter you choose will depend on your needs, preferences and the financial commitment you are willing to make. Lancaster said he uses a Big Berkey gravity-fed activated charcoal filter.

“If you’ve got problems on your roof, lead flashing or air contamination, it’s really good for those things,” he said.

If you plan to drink your rainwater, Lancaster said you should also be sure to choose safe materials and paints for your roof and gutters.

“Choose non-toxic roofing materials and gutter materials,” Lancaster warned. “[Choosing paint with] no lead flashing is a big one. Paint should be toxin-free or biocide-free — [biocides] inhibit moss and growth and stuff — because that’s going to go in your water.”

Lancaster said you do not have to filter the rainwater you use to irrigate your plants, or to wash yourself and other items.

How to choose a rainwater tank

The most important aspect of choosing a rainwater catchment system, the apparatus that will gather and divert the rainwater you collect, is its size.

“In the water harvesting world, rain barrels are often referred to as the gateway drug into waterwise landscaping,” McCann said. “They get homeowners excited about harvesting rainwater but they are kind of impractical when you think about the size. A 50 gallon rain barrel is not much at all.”

Lancaster also advised against small rainwater catchment systems.

“They’re just toys,” he scoffed. “They fill up really quick and empty really quick. If you’re really looking to use rainwater as a significant water source, you have to have a tank large enough to capture a usable amount that’s going to make a difference.”

McCann said that there are some useful equations and online calculators that help you to estimate the size of the rainwater tank that you need.

“My rule of thumb is that if you’re going to size a tank, the absolute smallest it should be is to handle all the water coming off the surface you’re collecting on in a typical spring rain,” Lancaster said.

Lancaster said he recommends buying a tank that is even larger than that, just to be sure you have all the space you need.

“I want the tank to handle at least 25 percent of all the rain falling on my collection surface in a rainy season,” he explained. “Start with 25 percent because you will be emptying the tank repeatedly through the rainy season and creating more capacity.”

Materials is also a consideration when you are picking your tank.

“In terms of materials, it depends on you and your site,” Lancaster said. “Plastic tanks can be cheap and easy to install and carry but they don’t last as long. Depend son how you install it, in full sun or not.”

Metal tanks last longer, and are often lined with plastic. Lancaster said that concrete is great for underground tanks.

“You can seal it with potable-grade sealers,” he said. “The great thing about concrete is that it doesn’t burn, double as firebreak.”

Rainwater tanks also come with a variety of screen styles. Screens that sit flat on rain tank are common, but McCann advised against recommend them.

“If your rain tank is above eye level, you’re not going to easily see the screen,” she said. “If it’s out of sight, a lot of times, it’s out of mind.”

McCann recommended a screen called a rain head, which is situated at an angle and comes down off the spout of the tank.

“Because it’s at an angle, when you walk by you can easily see debris and wipe it off,” she explained. “As a homeowner, you have to consciously think about looking for debris if you can’t see it when you walk by.”

Placing your rainwater tank

Lancaster said that when it comes to placing his tank, he tries to put it in the spot where it will collect the most water and also at elevation so that the water that the tank collects can easily flow out.

“I want my tank so it’s low enough to collect water from the roof but also as high as I can so it’s gravity-fed as much as possible,” he explained.

Your climate also matters for where you put your rain tank.

“If you’re in a colder climate, want to make sure putting tank on the south side of tree so it’s getting winter sun,” Lancaster advised.

You also want to put your tank in a spot that will not cause algae build up.

“Algae grows primarily with sunlight,” McCann said. “When you’re experiencing algae, you either have a transparent tank or there’s an opening at the top where a lot of sunlight is getting in. The best way to prevent algae is to make sure it’s dark where that water is being stored.”

You can also choose a location for your tank that will give it multiple uses, such as a privacy screen, structural element or a pillar of a covered porch.

“I would challenge one to think how that tank can be more than a water storage vessel,” Lacaster said.

Other methods of harvesting rainwater

Not all rainwater harvesting techniques require a tank, though.

“You can do it in a way where you don’t even need a tank,” Lancaster said. “The cost of the endeavor can be no more than the price of a shovel and some sweat.”

Lancaster said rain gardens are another great way to harvest and utilize the precipitation that collects on your land.

“My approach is [to] make this as integrated and multifunctional as possible,” he said. “Let’s prioritize edibles.”

Lancaster’s website, Rainwater Harvesting, has a variety of free resources to help you get started planning a rain garden that best utilizes your resources and helps you grow food.

If you plan your landscaping with harvesting rainwater in mind, it will save you lots of time and money on your garden.

“Here’s the mantra: plant the rain before you plant any plant,” Lancaster said. “Right off the bat, you’re setting yourself on a path where free onsite water is going to be your primary irrigation source.”

The challenges of collecting rainwater

New rainwater collectors often do not think of what will happen when their tanks overflow.

“A lot of people go right to thinking of a tank,” Lancaster said. “Here’s a thing people rarely think of: where will you address the overflow of the tank and how will you do so in a way that will not waste resources?”

McCann recommended using an overflow pipe coming out of the top of the tank to flow into a garden or part of the landscaping instead of out into street.

“The biggest mistake I’ve seen homeowners make when harvesting rainwater in a rain tank or barrel is improper overflow and improper screen,” McCann said. “Just make sure that the overflow is going somewhere useful — not just down a paved driveway.”

Standing water in the rainwater tank can also attract mosquitoes.

“When you have a gaping hole or any hole in the top of your rain tank, it’s a mosquito breeding ground,” McCann said. “You want to make sure you have proper screening systems.”

“If you have a system that’s generating mosquitoes you have a bad system,” Lancaster added. “All tanks should be screened off from all insects and critters. There’s a chance that mosquitoes get in, lay in gutters, eggs go through screen, but as long as you have screens they can’t get out.”

Ultimately, though, Lancaster, who lives on rainwater as his sole water source, believes that navigating these challenges is worth it.

“You’ll wake up at three in the morning to check out have everything is working because it’s so fun,” he chuckled.



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