Our Water Management Strategy for living Off-Grid in the Desert

In this post I would like to share with you our permaculture strategy for managing water on our property in the desert. It will provide an overview of the entire system, with future posts discussing and explaining individual components of the system in more detail.

Our Context:

The property is an urban-zoned lot of 5000 m², located in the brittle desert environment on the Pacific coast of Baja California Sur, Mexico. At the time of writing, this specific area is very sparsely developed, with only a few buildings spread out across a large grid network of gravel roads forming a square pattern on the landscape. The property is currently completely off-grid, as services are only due to be installed sometime in the coming years.
Our goal is to develop the property in such a way that our water systems are as economical, efficient and self-sustainable as possible, whilst providing water security for everything living on the property. This includes human, animal and extensive plant systems.

Sources of Water:

1) Trucks: The majority of the properties in the area get water delivered by trucks. This water is mainly well water, supplied by private individuals or local communities, and sold to homeowners whenever needed. This will be the starting point for us, as it is the only available option, initially. It is far from ideal, and our goal is to minimise our reliance on this source as much, and as quickly, as possible. In an emergency though, it could be beneficial to have this option available to us, as this system is already well established here.

2) Rain: The second source of water in the area is from rainfall. At an historical average of 200mm per year (about 7,8 inches), with wildly varying annual maximum and minimum figures, this is not very much. It is also sporadic, and quite unreliable. However, when it rains, it pours (potentially)! This is especially true during hurricane season, where figures of up to 200mm within 24 hours have been recorded.

3) Other forms of Precipitation: In desert environments, every drop counts. Therefore any moisture obtained from smaller sources of precipitation such as fog, dew, mists and humidity should be taken into account. They make up a smaller portion of total water supply, but can potentially offer a more regular and reliable source. Technology, both ancient and modern, enables us to harvest water from these sources. Some plants are also very well adapted for this purpose, and as such can be a very valuable addition to the garden and to other plants in their vicinity.

My Design Approach:
As the property is off-grid, with no access to consistently flowing water, we will need to store water on site, and I will discuss several options for this.
Rainfall is a key component of my design, as it provides the biggest quantities of clean water, and as such it will account for the majority of our water needs here. Investing time and money into developing adequate and appropriate rainwater harvesting systems will yield the biggest returns in terms of achieving our plans of creating an economical, efficient and self-sustainable water supply in this desert environment.
Another absolutely vital part of my design deals with the use of water once we have it available on site. How do we reduce water consumption, and how do we use it in the most efficient way possible, both in the house and in the garden.

Water Storage:
We will store water in two ways on our property; in the ground, and above the ground.

’In the ground’ refers to storing water in the soil, where it is available and easily accessible for the plants. This is the cheapest form of water storage, and although it does not directly provide for the water needs of humans, it has the potential to greatly reduce the need for watering the garden, and therefore we would be saving that water for our personal needs.

’Above the ground’ storage includes ponds and tanks. Ponds are not a great long term storage solution for water storage in the desert due to the high evaporation rates in this dry climate. They can be very useful though, as they can capture a lot of surface run-off in big rain events, giving us the opportunity to then direct the water into more appropriate storage solutions. Ponds are also comparatively easy and cheap to create.

Tanks offer a secure and reliable storage for water. We will use a combination of plastic and concrete / ferro-cement tanks. Each of these have their pro’s and con’s, and we will be using the strengths of each type of tank to make up for the weaknesses of others, and in doing so, create a very secure and safe water supply on our site.

Rainwater Harvesting:
Our goal here is to capture as much potable and run-off water during the sporadic rain events, and store that water in the storage systems described above.

For storing water in the ground, we need to slow it down, spread it evenly across a larger surface, and let it sink in over time. ‘Keep the water from running, and make it crawl.’
To do this effectively, we can make use of small-scale earthworks such as swales, trenches, diversion drains, soakage pits, etc. The strategy is to implement these systems by starting on the highest point on the property, and gradually work your way down to the lowest point, where the water would then be leaving the system.
The potential energy of water is at its greatest on the highest point, and therefore we aim at keeping the water here as much as possible.

For storing water above the ground, we collect water falling on to hard surfaces such roofs and roads. Where you collect your water from will determine how clean it is, and what it will be suitably used for. ‘Clean’ surfaces such as roofs make for great collection points of potable water, perfectly safe for human consumption.
Additionally, adequate, and often quite simple filtration and purification systems could turn more ‘contaminated’ water into clean potable water, also safe for human consumption.

Calculating rainwater harvesting potential:
Here is the formula for calculating the maximum amount of water you could harvest from a given surface:

surface area (m²) x rainfall amount (mm) = quantity of maximum water harvesting potential (litres)

To calculate how much we can realistically harvest from this surface, we need to know the ‘runoff coefficient’ of the surface. The runoff coefficient is a value which determines the percentage of water that can run-off a given surface. For example, a lawn will have a lower runoff coefficient than a roof, as it absorbs much more of the water.
The numbers for different types of surfaces are easily found online.

This formula will then give you a realistic estimate of actual rainwater harvesting potential of a given surface:

quantity of maximum water harvesting potential (litres) x runoff coefficient of the surface = actual rainwater harvesting potential

Harvesting Water from other forms of Precipitation:
As stated earlier, all sources of water are important in the desert.
The possibility to harvest water from ‘minor’ sources such as mist, dew, condensation and humidity does exist, and I will cover them detail in future posts.

Reducing water use in the House:
The list of options we have to reduce our water consumption in the house is quite long, but here are a few approaches:

1) Using compost instead of flush toilets. The average flush toilet uses about 30 000 (yes, 30 thousand) litres of water per person each year. By using compost toilets we significantly reduce the water use and the monthly water bill. We also avoid the negative ecological impacts associated with flush toilets. More of this in another post though.

2) Low-Flow fittings on taps and showers account for significant water savings, even without reducing the actual ‘use time’.

3) Water efficient washing machines are available.

4) Optimising workflows of daily tasks such as washing dishes and brushing teeth also add up to significant reductions.

Reducing water use in the Garden:
Here we implement three main strategies, and they are to reduce evaporation, increase soil organic matter and plant appropriately adapted species according to the microclimates (and their subsequent availability of moisture) on your property.

In theory, these strategies are quite simple. In practice, there are a lot of variables, and a working solution will depend the combination of variables that exist for each specific location within your garden, at any given time. Gardens often exist as complex living systems, and as such they keep changing and evolving, and therefore we need to actively adjust and adapt our solutions.

I look forward to sharing these sort of evolutions and changes in our garden with you!

Increasing Water Efficiency:
This is a critical part of my design for our property, as this strategy can massively reduce our overall water consumption.
The idea is simple:
‘How can I maximise the use of each litre of water?’

Here is a oversimplified, but adequate, example:

I use 5 litres of water to wash our dishes. That water flows into a worm-farm, where solids and fats stay behind and get broken down by earthworms, who then provide very high quality worm castings for our perennial and annual food producing plant systems. From the worm-farm, the water then flows into our biological grey-water purification system. Here, the specifically selected water-loving plants such as reeds filter out all the access nutrients and pollutants, and ‘lock them up’ with carbon in a process we all know as ‘growing’. These plants are occasionally harvested and used as mulch, compost material, construction materials, etc. A useful resource in a permaculture garden! The water, now cleaned, is then directed into a small pond, which is both beautiful to look at, and also a highly productive ecosystem in itself. Perhaps we skip the pond, and instead just water the garden? The possibilities are endless.
Granted, a small amount of the water is ‘lost’ at each stage of this process, but the big majority of it makes it through the entire system. This is a very efficient and integrated system.

In addition to this, we just saved those 5 litres of dish water from going down the drain and into a septic system, where it would then be mixed and further contaminated with black water (sewage).

In a conventional system, we would be using 5 litres for washing dishes, then another 5 litres for the worm-farm, another 5 litres for growing reeds, another 5…. You get the idea. It is highly inefficient, water intensive and unnecessarily costly.

Purifying and re-using ‘waste water’ will be a huge aspect of our water management strategy, and by doing so we will be able to get multiple uses out of the same water before it leaves our system.
We do this by installing biological grey water purification systems.

Conclusion:
Firstly, if you have made it this far in this post, thank you! You made writing it all worth it!
Secondly, you will undoubtedly have noticed that our water management strategy for our permaculture property in the desert is very extensive. This system takes a lot of time to set up and implement in its entirety.
When I design a system such as this, it gives me a general guide for the long run. I then go and implement all the individual parts of the system, as and when needed. This is a helpful approach because it breaks down everything into small and manageable parts, whilst making sure that the end result is what I intended to achieve all along.

I hope you found this information helpful and informative. Let me know in the comments what you think. Also feel free to ask any questions you may have.

I will keep posting more detailed information about the individual systems mentioned above, and also share our progress as I go through the design process and then as we start the actual development of our property.

Thank you again for reading my thoughts, and I hope to see you again on the next one.

With Love,
Shawn.