Water Wise Gardening: Capturing and Saving Water
Updated: Apr 27
Let's talk everything water in the garden!
Gardens are one of the highest water users in residential areas, especially in summer. It takes an enormous amount of the wet stuff to keep that grass lush and green in the middle of a summer heat wave and to grow veggies successfully, requires a lot of that wet stuff too. So how do we preserve this precious resource? There are numerous things, both big and small, that can make a difference. You don't have to do them all, but any little bit helps. This is the first in a series of three articles looking at water conservation in the garden. We will begin with how to capture and save water.
Here in southern Alberta, we are in an extremely dry environment. In fact, we are very close to being classified as desert. Part of this is due to lower amounts of rain and snow, but a large portion of it is due to the huge amount of evaporation we experience here. Our high winds in summer and chinook winds in winter dry up precipitation like crazy! So, it just makes sense to use rainwater, use less water in the garden whenever we can, and choose plants that are drought tolerant.
Why Should I Bother When I Can Just Turn On The Tap?
Well, for one thing, rainwater is way better for your plants than tap water. It doesn't contain chlorine or other harmful-to-plants chemicals; it is at the perfect temperature for your plants and it is far softer than the water we get out of the tap (here in Calgary we have very hard tap water). Did I mention it is free too? Up to 30% of your annual water bill can come from just watering your yard. Not only that, capturing water instead of allowing it to enter our storm water systems reduces erosion, cuts down on flooding and decreases the amount of pollutants that enter our waterways. Have I convinced you yet?
There are two main ways for you to retain that liquid that falls from the sky. You can hold it in containers or you can utilize mother earth's extra large storage container: the ground. We are going to look at both of these methods.
How Much Rain Do I Actually Get?
In order to determine the best way to hold precipitation, it is helpful to know how much we actually get. To do this, we need to look up a couple of statistics for our area. I like to use two different amounts: the total rainfall in our wettest month (here it is June with 3.14") and the maximum amount of precipitation in an extreme daily rain event (the historic maximum amount of rain to fall within a 24 hour period: 3.75" for Calgary). This will ensure we have both enough room to store the water in a huge rainstorm event, and the rainwater over our wettest long-term period to be available during the height of the growing season. You can find these climate normals for your Canadian location at https://eldoradoweather.com/canada/climate2/alberta-climate2.html (for Alberta, but just use the pull down menu for other provinces).
Let's look at an example home:
determine your roof area by using the total square feet of your main floor (let's use a 1200 sq.ft. home)
multiply that by either your extreme daily rain event or largest total monthly rainfall, whichever is larger (3.75" x 1200 = 4500)
divide by 12 to get cubic feet of rain (7500/12 = 375 cubic feet)
multiply by 7.5 to get gallons (375 x 7.5 = 2813 gallons)
divide by the number of downspouts (let's assume four in this example) on the home (2813/4 = 703 gallons)
therefore, each downspout should ideally have a storage container of approximately 700 gallons (2,650L)
That is a lot of free water you can utilize! You can make this even more precise if you know exactly what proportion of your roof drains to each downspout (they are probably not all equal). This will vary based on roof shape and style. You can also do this same calculation for your garage or any other buildings on your site such as a greenhouse or shed.
Rainwater Storage Containers
Standard water barrels are around 50 gallons. That's not quite 700 gallons is it? If you want to store as much as possible, you can link multiple rain barrels together with a hose kit (usually available wherever you buy your rain barrel). Another option is to get something bigger than a barrel. I use IBC totes in my yard. They are 1000L (264 gallons) each and are often available used at a decent price (ensure they are food grade and haven't been used for anything toxic before you buy!). There are also numerous other storage options out there from huge underground cisterns to barely noticeable slimline tanks, to containers perfectly sized to fit under your deck.
Must Haves for Rain Tanks
There are a couple of additional things to think about before you buy a rain storage container:
It absolutely must have an overflow that can be directed away from your house. You want this to be at least 1.5m from your foundation. Once your container is full, you need somewhere for that excess water to go and you don't want it flowing over the sides of your container.
It must be opaque so algae does not grow.
It must be sealed so it doesn't leak and have a screen or something similar over the opening where water enters. This prevents mosquitos from laying eggs in the water and prevents children or small animals (like squirrels) from drowning.
You need a drain or tap of some kind so that you can use the water in your container. Brass is best in terms of longevity and outdoor resilience.
Additional Items for Rain Tanks
There are also a few good-to-have items or things to think about before installing your rain storage container:
Raising your container higher above the ground will increase the water pressure coming out of the tap. If the water in your barrel is at a lower elevation than the end of the hose connected to the barrel, it will not flow well at all. Also, keep in mind water is super heavy! If you are going to raise your container, its foundation must be very strong and stable.
A diverter attached to your downspout will allow you to change the direction of water from your storage container to the downspout (and vice versa). This way you don't need to unhook your rain barrel from your downspout every fall and then reinstall it every spring. All you do is flip the switch on the diverter so water goes to the downspout instead.
A first flush valve pulls off the first bit of water from a rain event so it doesn't enter your storage container. Oftentimes, the very first bit of water coming off your roof is pretty dirty (especially if you have an older roof that sheds asphalt bits and debris). Keep in mind you do need to empty the valve after every rain event, as it only fills if it is empty. If you don't think you can reliably empty it, don't bother installing one.
A filter prevents debris from entering the container. It too must be cleaned occasionally, but not as often as a first flush valve must be emptied.
No matter how you set up your rain storage container, in our climate it must be emptied (and be kept empty) for the winter. Frozen water in containers, equals busted containers. If there is an opening on the top that snow and water can enter, it is helpful to flip your container over for the cold season. You will need to find an alternative way for water to drain away from your house. Here in Calgary, we have some remarkably warm spells in winter (chinooks) and rain or significant amounts of melting snow coming off your roof will need to be dealt with. Remove any metal fittings such as taps or drains and store inside for the winter too.
This is the rain barrel accessory I use in my space. It is a multifunctional downspout device that I have attached to my IBC tote. It is a filter and diverter all in one. All I do in the winter is drain my tote, remove and rinse the filter and turn the dial from fill to divert. Water from my downspout goes into the overflow (the hose on the bottom which drains into a swale) instead of into the tank. I don't have to detach or take apart anything. And it is all made from recycled materials. Pretty slick, right? I originally bought these from Aquabarrel, but have recently learned that they have discontinued them due to low demand. Feel free to contact them and ask them to start manufacturing them again as I have! I, for one, would love to purchase more! See the link to Aquabarrel's site in the references below.
Slow, Spread and Sink Water
Collecting rainwater that falls on our roofs is something we have all seen or heard of, but what about the water that falls on the rest of our landscape? What about snow that falls all winter long? We can utilize this water too! All we need to do is determine how water currently moves on our site during a rain event.
New homes are required to have their lots sloped to move water as quickly as possible off the site to storm drains. Here in Calgary, you need a Final Grade Certificate to prove this is done before your new home is approved by the city. This prevents potentially wet basements, boggy spots in your yard, and all your water running into your neighbour's yard. There is a problem with this however. If we get rid of the water as fast as possible, we don't get to use any of it for ourselves. Not only that, when we do get significant rainfalls, storm drains are often overwhelmed by runoff from large tracts of hard surfaces and residential areas that are designed to move that water to the storm drains immediately.
The answer is to slow down that water and sink it! We are not directing the water anywhere different, we are just making that flow of water much slower, giving it the opportunity to sink into our soils. That is, after all, where it is needed most. Water is absorbed deep into the ground where it is easily available to your plants throughout the year. The soil in your yard is a much larger rain storage unit than any tote or barrel ever could be. And you won't have to empty it in winter time either! When done properly, ground water and aquifers will begin to replenish after about 7 years of sinking water. What a great thing to do for the environment! That being said, it is important to note that we do not want to sink water into the soil right beside our house foundations. Big no-no. All surfaces next to your home should be sloped so that water drains away from those foundations by at least 2%. We don't want any flooded basements here.
First and foremost, we can't sink water into the soil if there is no soil available. Asphalt or concrete driveways and large expanses of pavers are impermeable and water simply runs off of them. Designing with less of these hard surfaces, or using hard surfaces that are purposefully made with "holes" so that water can find a way to the soil underneath (often called turfstone pavers), can help. This allows water that falls on your yard to sink into your soil, instead of being quickly moved over a non-porous surface toward the street or drain.
There are a number of different ways of contouring the earth to facilitate slowing and sinking of water as it moves over our landscape. Once again, we are not significantly changing where water is flowing to, we are slowing the flow of water to allow it to soak into the soil. Swales, berms, terraces and raingardens are all examples of earthworks for water management, each with varying benefits and uses. This doesn't have to be complicated. Slopes equal runoff. The steeper the slope, the faster water will move. On level ground, water will sit. If that ground is permeable, that water will soak in. If it is not permeable, it will pool. It is well worth the time to get out there in the middle of a rainstorm and observe your land! See where water is currently moving and think about how to maximize the use of all that water! Remember, that if you are going to utilize a number of earthworks, it is always a good idea to consult with a landscape professional.
In the permaculture world, swales are shallow, low trenches in the ground designed to encourage the accumulation of rain during storms and hold it for a few hours or days to let it infiltrate into the soil. They are built on contour, which means the bottom of the swale is exactly level all along its length. This ensures the water evenly spreads out along the entire swale before overflowing. The swale also must have a level spillway so that, in times when water is overabundant, it can release safely and slowly to an appropriate location without causing erosion. Often, swales are filled with loose material such as mulch to allow them to function as a pathway too. We use swales as tree planting systems in the permaculture garden. Trees usually need a whole lot of water, and swales can easily provide a concentrated supply. In our climate, trees are most often planted on the downward side of the swale, on the far side of the berm (see illustration below).
Drainage swales are a different beast altogether. They are used for moving water from one location to another and have sloped bottoms instead of level ones. They are similar to trench drains (see French drains below).
A berm is simply a rounded mound of soil (or rocks and logs), built upon an otherwise level patch of land. They are used to divert water runoff around the things that you want to protect. In permaculture, berms are often located on the downhill side of swales and are made using the soil removed to make the swale (see illustration above). Raised beds are also a type of berm, they just have flat surfaces and rectangular shapes. Very small berms are also commonly used to form shallow bowl depressions around trees to trap water within the tree's root zone.
Terraces are short walls on steep hillsides that create flat land areas, slowing and stabilizing water runoff. Think of traditional Asian rice paddies. Note that any retaining walls on very steep slopes and higher than 4 feet will need advice from an engineer.
A French drain is a sloped trench filled with a perforated pipe and gravel that allows water to drain through the pipe to a different location. The weeping tile around the base of our foundations, which are typical here, are technically a type of French drain. French drains are subsurface structures while trench drains are surface ones. Drains are best used in soil that is prone to frequent saturation from rain or flooding or in areas we do not want any water at all to collect (such as beside our foundation walls).
Rain gardens are an area of shrubs, perennials, and flowers planted within a depression in the landscape. They are designed to temporarily hold and soak in rain water runoff from lawns and downspouts, and are most often located on the lowest elevation point of a property. Rain gardens are not only used for soaking water into the soil, they are also super effective at cleaning that water too. Up to 90% of nutrients and chemicals and up to 80% of sediments can be removed from runoff using a rain garden. That is really good news for our storm water systems! It is important to note that rain gardens are not ponds or wetlands. They are designed to only hold water for 12 - 48 hours following a rainfall event. This is a good thing, as it prevents mosquitoes from laying eggs and hatching in long standing water. We have enough mosquitoes here as it is, thank you.
Plants for rain gardens need to be able to handle flooding, but they also need to be drought tolerant for those in-between-rain periods. Thankfully, there are a great many plants that are hardy here in the Calgary area (Canadian zone 3) that have these characteristics. Our native prairie grasses are a prime example, but there are loads of pretty flowers and shrubs that work too.
For sunny rain gardens:
Blue flag iris (Iris versicolor)
Feather Reed Grass (Calamagrostis acutiflora)
Joe Pye Weed (Eupatorium maculatum)
Tufted Hair Grass (Deschampsia cespitosa) - native
New England Aster (Aster novae-angliae)
Showy Milkweed aka Butterfly Weed (Asclepias tuberosa) - native
Sneezeweed (Helenium autumnale)
Goldenrod (Solidago rugose)
Liatris (Liatris spicata) - native
Black-eyed Susan (Rudebeckia fulgida)
Big Betony (Stachys macrantha)
Beardtongue (Penstemon digitalis)
Purple Coneflower (Echinacea purpurea)
Sedum (Sedum spectabile)
Russian Sage - (Perovskia atriplicifolia)
Raspberry - edible bramble
Dogwood (Cornus) - native shrub, many varieties
Spirea - shrub
Dwarf birch (Betula nana)- native shrub
any of the Willows (Salix) - shrubs and trees, some native
Currants and Gooseberries (Ribes) - edible shrub
Potentilla (Potentila fruticosa) - shrub
For shadier rain gardens:
Creeping Jenny (Lysimachia nummularia)
Ligularia (Ligularia stenocephala)
Ostrich Fern (Matteuccia struthiopteris)
Bearberry or Kinnikinic (Arctostaphylos uva-ursi)
Coralbells (Heuchera sanguinea)
Foamflower (Tiarella cordifolia)
Jacob's Ladder (Polemonium reptans)
Purple Meadowrue (Thalictrum dasycarpum)
Columbine (Aquilegia canadensis)
Pink Turtlehead (Chelone lyonii)
Astilbe (Astilbe) - many varieties
Snowberry (Symphoricarpos albus) - spreading shrub
Arrowwood (Viburnum dentatum) - shrub
So what does this look like in a real yard? Below is an example of a property I recently designed. It has three swales that slow and sink water from the patios, garage downspouts and the rain barrel overflows by the house. Swale 1 has a spillway (W1 on the sketch) that allows any overflow to empty into swale 2. Similarly, swale 2 has a spillway to swale 3. Swale 3's spillway empties into a raingarden which is located on the lowest point of the property. If for some reason we get a hundred year flood and all of these water storing devices were full, excess water would be directed to the roadside ditch around the perimeter of the property via another spillway (W4). Yes, this looks like a huge amount of expensive earth moving and digging, but in reality, it is not as much as it looks. These swales are only 10" deep and 3' wide. They are also filled with mulch and used as pathways throughout this garden (why we chose 3' wide swales) so you don't even notice that water conservation is happening right under your feet. Trees were also planted on the downward side of the swales to take advantage of the available water (so much less maintenance this way!). The rain garden is a mere 6" deep and backfilled with loose, well-draining soil. It is packed with gorgeous perennial plants and shrubs and has a small seating area beside it. The owner uses it as a quiet get away with a fantastic view and also as a source for cut flowers for the home.
Saving the water that comes free to us from the sky doesn't have to look stark and utilitarian! The point of that water is to ultimately feed our trees, shrubs and flowers after all. With a little imagination and planning you can design a space that is both water wise and absolutely beautiful!
So that was how to capture and save rainwater. I hope I didn't scare you off with the possible scale of this. Remember, even small bits help! Next article we are going to talk about how we can reduce water usage in the garden (think xeriscaping and other water reduction strategies). After that we will learn how plants survive low water periods and give you lots of examples of drought tolerant plants that work fantastically well in our growing zone.
Yummy gardening everyone!
Other Articles In This Series
References & Resources
Canadian climate data https://eldoradoweather.com/canada/climate2/alberta-climate2.html
City of Calgary Rain Barrel program information https://www.calgary.ca/uep/water/water-conservation/lawn-and-garden/water-wise-gardening-and-plants/rainbarrel.html
Aquabarrel for all your rainwater harvesting supplies https://www.aquabarrel.com/
Lancaster, Brad "Rainwater Harvesting for Drylands and Beyond. Volume 1 & 2. 3rd Edition" 2019, Rainsource Press, Tuscon, Arizona, USA
Mollison, Bill "Permaculture. A Designer's Manual" 1988, Tagari Publications, Sisters Creek, Tasmania, Australia
Avis, Rob and Avis, Michelle "Essential Rainwater Harvesting. A Guide to Home-Scale System Design" 2019, New Society Publishers, Gabriola Island, BC, Canada
City of Calgary Rain Garden information https://www.calgary.ca/uep/water/construction-projects/stormwater-quality-retrofit-program/rain-garden-calgary.html
Burnco for hardscaping products such as Turfstone permeable pavers https://www.burncolandscape.com/