How rainwater is worth a lot of money

Precipitation of our area

If have never before really considered how much water costs. I know that store-bought water is basically a scam making people pay horrendous amounts of money for bottling something that belongs to everybody. We already talked about how filtering your own water enables you to live much cheaper.

This post starts with the trees

Today I researched the water needs of the trees that we are going to plant early next year. It turns out that generally, trees need around 80 liters per week in their first 1 – 2 years.

We are planning to plant at least 500 trees, that alone means that we will need to cover 160,000 liters each month. Luckily, we got access to irrigation and pay around 28 cents per 1000 liters, which would cost around 44.80 € a month.

But do we even need irrigation?

This is exactly what I am trying to find out. If we can, I would like to not lay down hundreds of meters of tubing and save money by not installing an irrigation system to water each and every tree.

How much does it rain?

While we don’t have a dam, a pond nor a stream, we certainly do have rain. In fact, we are blessed with around 500 mm of rain each year on average. The wettest months being May, September and October, and the driest June, July, and August.

There are two great sources I use for such data: to get a quick summary and to get detailed historical reports.

I was very curious how much water is raining down onto our property. Knowing the yearly average, it is an easy task to calculate how much rainfall we get on our whole land and found that it is around 15 million liters a year! That’s enough water to fill 6 Olympic sized swimming pools. In monetary terms, that’s 4200 € a year that rains onto our land.

Is it enough?

In order to answer the question properly, I created a spreadsheet called Tree Satisfaction that you can view and copy it into your own library. You can use it for your own planning. You can find a step-by-step guide here.

Let’s start optimistic and assume we collect 100% rainwater and nothing slips through our fingers.

We calculate that a tree occupies a circle with a 2 m radius. By using the good old formula of calculating the area of a circle (π×r²) we get 12.56 m².

In a year, the tree would then receive around 6.900 liters. In a week that would make around 132 liters. That’s above 80 liters and that’s already a good sign.

In order to combine it all together, I will use the term tree satisfaction. It’s a metric that tells us, how happy trees are based on how much water they have available in the soil.

Tree satisfaction in a perfect world
When they receive water, the satisfaction rises (green line). When the soil is completely dry, the satisfaction is basically 0.

Let’s be realistic

Of course, it’s impossible to collect 100% and keep it. Water runs off, it evaporates and other plants want to drink it too.

A more realistic example of tree satisfaction
A more realistic example of tree satisfaction

Yelp! That’s a little bit frightening. Those red triangles are sad tree days, it basically shows the days the trees would not have any water available and would be sad.

Luckily, permaculture design offers many ways to mitigate droughts.

Combating run-off

One of the most common features you see in Permaculture Design is the Swale. Swales help reducing run-off by holding it on contour. The water then has enough time to soak into the soil. Once underground, it runs slowly and is protected from the sun and wind so it does not evaporate.

We also consider doing micro earthworks such as building tiny dams around the trees. Our options are: loosening the soil around for quicker soaking, building mini damns around the trees and digging small pans before planting. This way we directly hold the water in place, where we need it.

Combating evaporation

Water that is out in the open evaporates due to wind and the sun. And we have a lot of both. In our semi-arid climate, it is essential to curb evaporation.

To reduce evaporation by wind, we are going to install and plant windbreaks. On a small scale, we’re going to protect the seedling in their early stage by putting a plastic bottle around it. I am already going around town and collecting plastic bottles that are littering the landscape.

On a bigger scale, we are planting palm trees, cypress, shrubs, and other wind-resistant plants that will either slow down or lift the wind so our soil and plants are protected.

To reduce evaporation due to sunshine we will try to establish a quick ground cover and soon a shade-giving canopy (which is kind of a chicken and the egg situation right now). For this reason, we will plant fast-growing pioneer trees that should shade the soil within one or two years.

Locally we can place pebbles and rocks around the tree seedlings. Mulch is also a great option if we can source it for no to little money.

Tree satisfaction when applying water harvesting techniques
Tree satisfaction when applying water harvesting techniques

Theoretically, on paper at least, we can reduce the sad tree days but there are still some periods that will most likely require us to step in and water the trees ourselves.

Surviving the dry period

We think that by applying most of the designs we mentioned above, we should be able to get the trees established without much extra watering. After all, the pioneer species we selected are native to dry areas.

Yes, they do need care in their first years but they are hardy and capable to establish under bad conditions. Should we notice that the summer is too dry, we can still water them manually.

Should everything fail, we can always fall back to installing an irrigation system. This article explains many cost-efficient and effective methods.

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