Rainwater harvesting systems are a hot topic in gardening circles. As we become more aware of the value of water, gardeners want to collect rain and use it to water their plants. Not only does this make financial sense, but in many cases the quality of the water is much better than tap water. And it is great for the environment because it sends less water to the city for processing.
Along with any good idea comes a number of myths. In this post I will look at myths pertaining to the use and harvesting of rainwater.
Rainwater for Gardens
Let’s be clear about the scope of this review. I am strictly dealing with use of the water in the garden. This is not about using it for human or animal consumption. Having said that, collection for human consumption is done all over the world, its just my experience.
Stored Rainwater Goes Bad
A recent discussion on our Facebook group had several people comment such as “stored water deteriorates” and “standing water will go stale and should not be used in the garden”.
If you take a glass of tap water and let it sit out overnight, it does taste funny in the morning. This fact might lead people to think water goes stale.
The reason drinking water tastes different after sitting out is partially due to temperature. Most people like the taste of cold water better.
A lot of tap water has been treated with chlorine and humans like the taste of water better when it has a bit of chlorine added, but too much is not good. Chlorine is quite volatile and off-gases overnight, so water does not taste as good in the morning because it has lost its chlorine edge.
Water also absorbs gases from the air and these change the taste.
We think water is going stale because we don’t like the taste, but chemically it is just as fresh as when it was collected. Sitting water does not get stale or go bad on its own.
Stored Rainwater Needs to be Treated
There is the potential of getting some E coli in the water from roof runoff, mostly due to animal and bird feces. This is of no concern for plants except maybe vegetables, and then only if you apply the water to the part you eat. Watering the soil, as recommended, is no problem since your soil already contains E. coli.
Treating rainwater with chlorine has some limited value if you water the edible part of vegetables. This advice is mostly precautionary and probably makes very little difference. Picking veg with hands that have been working in the garden is just as big a problem and we don’t wash our hands with chlorine before harvesting.
You also have to remember that the same animals and birds that poop on your roof, also poop in the garden.
Harvested Rainwater Contains Heavy Metals
It is true that rainwater contains heavy metals, but the all important question is, what are their concentrations? After all, your soil also contains heavy metals, as does the fruits and vegetables you eat. Heavy metals are only a concern at higher levels.
One study that looked at backyard rain barrels found that “Heavy metals were well below federal irrigation standards for reclaimed water and posed minimal risk for irrigating a vegetable garden. ”
A study that looked at runoff from different kinds of roofs found very low levels of contaminates.
Another study, in Australia, grew various vegetables using artificially contaminated water and soil to see how various chemicals were absorbed by the plants. Some of these contaminates had a concentration that was 5,000 times higher than environmental levels. They found, “French beans and beet leaves, but not the beet root, had lead levels that exceeded Australia’s health guidelines. The kale in particular had lower levels of all of the metals, illustrating the wide variability in metal uptake among crops, and even into different parts of the same plant.” Most of the vegetables were still safe to eat. Keep in mind that they were testing an extreme case, far worse than the water from your roof.
There is little concern about heavy metals in harvested rainwater.
Rainwater Harvesting is Illegal
This idea was making the rounds a couple of years ago. Numerous people claimed harvesting rainwater was illegal in their state. When asked to provide evidence of this law, they couldn’t.
It turns out that Colorado did have a rainwater harvesting law on the books. That law was changed in 2016 so that homeowners are now allowed to have two rainwater harvesting barrels.
Other US states also have regulations in place for controlling and regulating the type of systems used, but most of these are for health and safety reasons. They don’t make water collection illegal.
Many jurisdictions are now encouraging the installation of rainwater harvesting system, because it is good for the environment, and it reduces their water processing costs. My town even sells rain barrels at a discount.
Storing Rainwater in Plastic Causes Toxins to Leach Into the Water
This is true. All plastic leaches toxins, even the plastic drinking bottles everybody loves. The UV light from the sun speeds up the degradation of plastic and exasperates the problem. The amount of chemicals leached by most plastic is minimal.
I have review the safety of using plastic as containers for growing vegetables. If a plastic is safe for growing them, it is also safe for collecting and storing water.
Stored Rainwater Breeds Mosquitoes
A properly designed rain barrel will be fitted with screens so that adult mosquitoes can’t lay eggs in the stored water. Breeding mosquitoes are not an issue in this case.
If you have an open barrel, consider using mosquito dunks, or simply add a couple of goldfish. They will not only get rid of the mosquito larvae, but also fertilize the water. If you do this, it is a good idea not to drain the barrels completely 🙂
Is Harvested Rainwater Safe?
Harvested rainwater is perfectly safe to use on all ornamental gardens, trees and shrubs.
If you are using it on vegetables, all the science indicates it is safe to use. There are some limited potential problems and most of these can be minimized or eliminated by doing the following.
Add a Diverter
A diverter is a device that diverts the initial wash-off from the roof away from your barrel. This water contains most of the pollutants from the roof and by keeping it out of the collection system, you end up with cleaner water.
The downside is that you collect less water.
Water The Soil, Not the Plants
Keep water off vegetable plants, and water only the soil. This will reduce any chance of pathogen contamination of the food.
Treat Reservoirs with Chlorine
Add one ounce of household unscented chlorine bleach to 55 gallons of water and wait 24 hours before use.
Use Containers That Are Opaque
Transparent containers allow too much light to get through, which can cause blue-green algae to grow. These plants can add toxins to the water. Opaque containers keep the light out and prevent them from growing.
I’m completely dependent on tank water for all purposes unless I buy (very expensive) water by truck from the nearest town, which I have to do during droughts. I find the taste of stored rainwater more pleasant than the town variety, which might only show we prefer what we are accustomed to.
I’ve never heard of anyone in the village (population c 500) getting sick from drinking tank water, let alone from using it on food crops.
Another excellent post.
Interesting looking at this from Australia, where over the last 20 years there has been a resurgence of interest in rainwater harvesting, indeed it is actually a requirement of new buildings that some rainwater is retained for toilet flushing and laundry use- by far the biggest user of water. This also means that you use water the whole year round, rather than summer. We often have water restrictions. Minimum sizes tend to be of the 1,000 gallon/ 5,000 litre size,which provides a decent buffer against dry weather, and many on larger blocks have 5,000 gallon or more size tanks. Mosquitoes become a problem if vents are not screened, and this is definitely a problem, especially with mosquito borne diseases that are spreading their range in Australia. We also have a lot of corrugated iron/ Zinc roofing here, but the studies I have seen show that it does not bioaccumulate. Old lead flashings, roof paint and fittings are a different matter for drinking water.
I wish governments in North America woke up and also changed the way we build homes. They should all be required to have cisterns, at least in areas that get enough rain.
But unfortunately, the environment is not yet a high priority.
Yeah the Australian experience is interesting! It is wonderful that our governments are so supportive. I considered tanks for our house in Canberra, but in crunching the numbers it just didn’t make much financial sense. We use tap water with drip irrigation, which I reckon is a much better first step for not using so much tap water in the garden in our hot summers. We will probably get tanks one day though.
On the mosquito note, this is definitely a concern. I think so many people are ignorant of the measures that need to be taken to prevent them breeding in a tank, or even just in standing water in the garden. I caught dengue fever whilst leading a school group in Cambodia and Laos last year, and I have never been more sick in my adult life. It took me a fair while to recover. We went past a dengue hospital while there and it was full of people. The type of mosquito responsible loves things like water tanks and standing water in a garden, and there have been massive outbreaks in urban areas across the tropics as a result.
WHere in Woodland, CA, my husband and I have a small suburban lot with a tiny vegetable garden in the backyard. We don’t get much rain, and what we do get we get in winter and spring. In late winter I collect rainwater in our 3 small-size plastic kiddie pools, which are also used by our grandchildren in summer. We have a slightly larger one with a crack on the bottom that doesn’t hold water anymore, and I flip it over and place it over one of the small ones as a cover. I use another of the small ones for washing my hands and garden tools, keeping an old toothbrush for scrubbing garden tools in it as well as a plastic Icee cup for directly watering the small vegetable plants around my garden that have sprouted in spring. I pour the water from the other small pool into the covered small pool. This way mosquitoes don’t breed in it and less insects fall in and drown in the open water, something that makes me feel remorseful.
The plants really like the quality of the rainwater and grow extra well as long as it lasts.
Hello,
I am just a bit confused on the E. Coli part. Is it something I should be worried about? I mean it is kind of impossible to keep some water from getting on some of the leaf vegetables I grow, such as lettuce or spinach. Where I live, the E. Coli would only really come from bird droppings, I guess. For this year, I already watered my lettuce and spinach in using rainwater collected in an opaque barrel. But, now your article has me thinking. Haha.
Best, ,
Robert
Most of the vegetable recalls you have heard about in recent years are due to E. Coli. But it is unclear, to me at least, how often this happens from home grown veg.
I mention it only to be clear about possible health risks. Personally, I don’t think it is a problem. I have no problem eating stuff right from the garden. I just wipe it off a bit on my dirty gardening cloths before I bite into that warm tomato.
It is best to wash veg from the garden. That eliminates a potential problem.
Undoubtedly the birds and squirrels and rats who run all over roofs have already left their calling cards in your garden, nothing is clean for long.
Humans are more at risk of too much cleanliness overall, with sanitizers and dishwashers and overuse of antibiotics (especially in agriculture) causing a very dangerous situation with antibiotic resistant microorganisms.
Children who grow up with pets are more healthy and robust because our micros need diversity – this is important for our immune systems. Just as children develop their immune systems by fighting illnesses, we all need to have exposure to the natural world. Our gut microbiome is much less diverse than previous generations and it impacts our health.
The kind of E-coli that kills came from the toxic environments of industrial food systems in the 1980’s and since then more and more dangerously evolved microorganisms are found there and in hospitals, and they rarely inform the public of the dangers they are creating with these modern environments!
I helped my father-in-law build a cistern out of plywood and 2×4’s. He lined it with fiberglass to make it water proof. This was in Ketchikan, Alaska, where they get 150 inches of rain. it collected the roof rain and was used to supplement toilet flushing and clothes washing, not drinking or bathing. it took pressure off of the not-quite-adequate well. No permit or anything. So why NOT utilize the water instead of letting it just end up in the bay? Covered to keep out dirt and leaves, but didn’t need to worry about sanitation. Still… not the same as a garden. They didn’t have one.
people can be so confused about water rights and thinking one little limit means so much more.
There have always been some limitation about water rights such that even Bugs Bunny encountered it in ‘Wet Hare’
https://www.dailymotion.com/video/x5zjrpn
https://en.wikipedia.org/wiki/Wet_Hare
Something people often forget is that your area needs enough rainfall to refill the rainbarrel during a time of the year when supply is meagre and demand is great. A rain barrel would not be worth the time, trouble and cost where I live. I’d need dozens. We get so little rain here from April through September, that water in one or two barrels would be used up by the end of April and then stand empty for the rest of the spring and summer. As long as we use city water judiciously, it is a much more practical way to go.
Isn’t it better to use what little you have than just let it run away? Our 4 rain barrels run dry most summers too. Every little bit helps.
One issue you did not address is the practicality of collecting rainwater for watering your garden. Is it a practical way to water? Does it in fact have any impact on water conservation? How far does a 55 gallon drum of rainwater go, in terms of adequate watering?
Is it practical? Depends on your point of view – many people think so. As prices on water go up, it will become even more “practical”.
Does it impact water conservation? Our cities are built to direct rain water away from the land on which our homes sit. This means underground rivers and aquifers are not being recharged properly, and this is leading to water shortages in many areas. Anything we can do to get the water back in the soil around the house is beneficial. Does one barrel make a difference? No. But 10 million do.
Robert, I am astounded that you, of all people, would use an argument such as “10 million do” to support the use of rain barrels. The whole premise of this website is to debunk mistaken beliefs is it not? If 10 million people think it’s great to add eggshells to their compost, does that make it advisable? I have to wonder if you have shares in a rain barrel company. The fact is that a single rain barrel doesn’t hold enough water to last more than a few weeks in a very small garden so unless enough rain falls to refill it regularly, it’s a waste of money.
I don’t think you took the time to understand my reply. The question is, does collecting water really make a difference – Does it impact water conservation?. One barrel doesn’t, but 10 million do.
I did not say it is cost effective. Saving the environment will cost us money in the short term.
I also did not say that 10 million users justifies the use of rain barrels, only that when a lot of people use them, it will impact water conservation.
We live on Vancouver Island and we run short of water in late August and September. We harvest about 30,000 gallons of rainwater over the winter off of our metal roof. We have 12 3,000 gallon capacity plastic cisterns to contain the rainwater. We use the harvested water every summer on our gardens, have minor algae problems. As each cistern is emptied we scrub clean to be ready to collect for winter rains. Also we have a ‘first flush’ diverter on the gutter downpipe. The key to success is to make sure everything is clean as possible.
I found no evidence that cleaning is important. Opaque containers don’t really grow algae.
Thanks for the article. I have some experience to share with rain barrels. When we moved into our home fifteen years ago, it didn’t have gutters or downspouts. The rain coming off the roof tended to pulverize the flowers we were trying to grow below, so we decided to get get gutters and downspouts. It was difficult to find free rain barrels in the color white but I did get some that had been used for a boat dock. At the time I don’t think there were automatic diverters on the market. I just bought some adapters and the gutter installers were willing to bring a 5 inch hole hole to terminate the downspouts into the rain barrels. The county horticulture expert said not to expect much water in the summer, but when it rained hard the water came shooting like a geyser from the gaps around the 5 inch fitting. I put in overflow holes near the top connected to garden hose and spigots at the bottom. I made bases out of treated lumber, filled them with gravel, and tied the rain barrels to them with wire to prevent them blowing away. I heard that one neighbor complained to the association about the looks of the rain barrels, but that person left the neighborhood and I didn’t hear anything else. With just the force of gravity there’s less water pressure through the spigot and hose at the bottom, and a person had to hold the hose end or wand lower than the level of water in the barrel. As a result we were not using the rainwater much for manual watering and I made some old garden hose into soaker hoses by drilling holes into them, and attached them to the spigots. This worked ok, but the spigots were often forgotten in the open position, so all the rainwater drained at one time. So the rain barrels were still not getting much use and I sold them for the cost of my materials.
I saw this article on automatic diverters, and it sounds like a prudent addition even without rain barrels:
https://www.waterpebble.com/best-rain-barrel-diverter-reviews/