When there is no water there is very little else. That is why water is, with good reason, the backbone of land-based Permaculture design. As designers, we observe and create opportunities to catch and store water. There are many options available to us: in the soil, in biomass and in ponds, dams, and tanks. There is lots of great tried and tested solutions out there that you could explore. Here I will share with you my views on ferro-cement tanks.
A ferro-cement tank is, in my experience, an interesting option when you need drinking-quality water but you are on a budget and have a bit of time for a DIY approach. It allows you to obtain a yield of rainwater from the roofs of buildings and store it.
Ferro-cement was invented around 1840 in France. Ferro-cement structures are created by constructing a frame from thin steel rods (rebar) that is then covered with a metal mesh to create the form of the structure. Then thin layers of sand and cement are plastered over, resulting in a hard, strong finish, ideal for a water tank. Nearly all land-based projects have a need for water storage in tanks and ferro-cement offers a long-term pragmatic solution
The advantage of ferro-cement is that it can potentially be applied in many contexts, including remote areas or hard to get to places where other options (pre-cast concrete, metal or large plastic tanks) are unrealistic and more expensive. This is because it is possible in most cases to transport small amounts of cement and some re-bar. Pockets of sand can be found in most soils, taken on a small scale from a river or purchased, making it relatively easy to acquire at low cost.
The tanks that I built are used for drinking water, harvested from the metal roof of a house located next to the tank. For catching drinking water use metal or tiled roofs and avoid thatch or wooden shingles. When the tank is finished the roof should be cleaned and a first flush system installed. This redirects the first part of the water coming out of the gutter away from the tank so any debris or leaves do not go to the tank (more about that in the designers manual).
As well as channeling rain water directly into your tank, you can also pump water into it. Depending on how the water will be used, different levels of care is needed when harvesting. For good quality water, install a fine screen to stop insects and debris getting into the water, and a cover to stop direct sunlight entering. To make cleaning easy, there needs to be a wash out pipe flush to the bottom of the tank.
It is a good idea to position the tank in a place that is shaded and easy to access. To maximise your harvest you can calculate the square meters of your roof and average rainfall in your area. There are several online calculators which make this easy. Then you will know the volume of the tank you can build. The tanks I built (shown in the photos) are 3000 liters and were built in workshops. If you build a tank of 1000 liters, it is still light enough to make it be portable.
Everything has its place and decisions are made based on context, climate, project goals and budget. I believe this is a great technique available to people in most circumstances, easy and inexpensive. It is truly versatile and many useful structures can be produced employing this technique from boats to sinks, roofs, and tanks for storing water, greywater filtering systems and aquaponics.
Matt Prosser is an international Permaculture designer, teacher, sustainable builder and co-founder of www.holisticprogressiondesigns.com. Matt will be teaching a certified course at the Alisler Yurdu project in Turkey. The course has been designed so participants leave inspired and empowered with practical know how that can be applied anywhere.
Get Your Hands Dirty: Sustainable Building & Permaculture workshop June 23 – 27: https://www.holisticprogressiondesigns.com/turkey-june-2017.html
Alişler Yurdu is is a exciting example of Permaculture and sustainable living in the Mediterranean. Set in a stunning location the project strives to inspire and empower harmonious, healthy and creative lives