It’s time to talk about water harvesting. Most conventional housing either has their water coming from a well or the water grid of the municipality in which it is located. Earthships don’t use either of these methods and we are going to discuss the how and the why of that here.
Earthships make use of cisterns at the back of the building to store the water that is used inside. You can see a cross section of one of the cisterns in this drawing.
Here is a top view showing five cisterns in the plans for this Earthship.
Why cisterns? Well there are several motivating factors at play here.
First of all, Earthships were designed to be built just about anywhere on the planet. With this in mind, an Earthship must be self-sufficient and independent. An Earthship takes care of itself and if you hook it up to a municipal water source you are then dependent on it for your water. If something happens to that water source, you are affected, just like everyone else connected to it, and you can’t do anything about it. Stories of communities that have had boiling requirements (huge energy usage there) for their water, or those close to fracking operations who can light their water on fire as it comes out of the pipes are a few issues that come to mind.
Water contamination is one thing, but you are also subject to how your municipality treats their water as well. Overuse of chlorine and fluoride can make city water disgusting, unpalatable and unhealthy, forcing many to buy bottled water which defeats the entire purpose of having municipal water in the first place. Why spend all that money on plumbing your house if you can’t drink the water?
What about being connected to a well? In some parts of the world, like where we live, this is very common and for the most part sustainable as we do get quite a bit of rain over the course of the year. However, there are still weaknesses in this setup. If you go through a dry spell where you don’t have any rain for a while, you have no idea how much water you have access to. Water underground generally moves and you can never be certain of how much water you have flowing into the bottom of your well or out of it. You’re also subject to all of the issues that comes with underground water: hard water, sulfur water or contaminated water caused by run-off from industrial farms or other pollution sources. Sometimes you have to go to extreme depths to get to a water source, meaning you’re going to spend more energy bringing it out of the ground.
In some parts of the world, so many wells have been dug in an area that all of the ground water has been drained and it won’t be coming back as those were ancient aquifers and don’t have any new water coming in. I also saw an interesting documentary on sink holes a while back. Water underground takes up a certain amount of space. If you drain that water, you create a large cavity under ground and sometimes the ground above just falls into it as there is nothing to keep holding it up. There was one incident in the state of Florida where two days of frost forced the citrus growers to continuously spray their crops with water for 48 hours. That pulled a lot of water out of the aquifers and in the week afterwards, they had 60 (yes six-zero) sink holes, some of which swallowed houses and their occupants.
I’d also like to point out a literary metaphor for drilling wells. Mosquitoes are well known in our part of the world, especially in May and June. They land on you, stick their proboscis in your skin and suck out your blood. We are doing the same thing with wells to the earth. We stick our long pipes in the ground and suck out the blood of mother earth. Do we really need to be poking so many holes in the earth?
Earthships, on the other hand, catch their water from the sky. This is why Earthships always have a roof that is designed to catch water. Global model Earthships use a metal roof. Other designs use concrete or plaster. Whatever you finish your roof with, make sure it doesn’t have any toxic elements in it that will contaminate your water. Incidentally, rain water is always soft.
I should mention here that you can still get polluted water from the sky, depending on where you are located. If you are downwind from a major polluter (e.g. east of Beijing, for instance), the rain water you get may have serious contaminants in it. My advice: don’t build there.
The first question I usually hear when I talk about this is: will you have enough? Having enough water is based on several variables: how much precipitation you get in a year, how much of it you can store, how big is the surface area of the roof of your Earthship and what are your usage metrics like. If you like to take four or five showers a day, even on a well you won’t have enough water. If you can sit down and calculate how much water you use in a week, multiply that by 52 so you can get your yearly usage, then you have some idea of how much water you need to be storing. If they can make it work in Taos, New Mexico where they only get 8-12″ (20-30cm) of precipitation a year, then you should be able to make it work in all but the driest places on earth. You just need to make sure that when it does rain, you catch as much of it as you can.
The other advantage of storing your water in cisterns is you can always go look and see just how much water you have. Additionally, if we ever got to a point where we weren’t getting any rain and the cisterns where hitting critical low, we could hire a water truck to go visit a lake or river and refill them. We do live in an area with a huge abundance of lakes and rivers. You couldn’t refill your well that way, though.
So, you catch a whole lot of water in your cisterns and now you want to use it in your house. How does that work?
All of the cisterns are joined together so the water you have will distribute itself evenly across all cisterns. One input line goes from the cisterns into the house, where upon it is connected to one of these.
This, in Earthship jargon, is called a WOM. A water organization module. This is the thing you need to take the water from your cisterns and turn it into usable water in your house. I have put numbered labels on the picture and I will give a description of each of them.
- Input. This is where the incoming line from the cisterns is connected, with an appropriate cutoff valve so you can turn off the water for WOM maintenance.
- 50 mesh (300μ) filter, used to protect the pump (see 3).
- DC water pump.
- Pressure switch.
- 500 mesh (28μ) filter.
- T-joint. The water that goes down from here branches into your hot and cold water that will be used for washing and bathing.
- 1000 mesh (15μ) filter.
- Ceramic drinking water filter (0.5μ or less)
- Drinking water output line
If you followed that, you saw that there are separate lines for drinking water and generic washing water. You don’t need to filter washing water as much as you do drinking water, thus the separation. All of the filters that are traditionally used in a WOM have filters that can be removed and cleaned without the need to replace them too often. Of course, if you build your own, you can use whatever components you like.
I should point out that if you are building one of these in Canada, you can’t use PVC connectors like what is shown in the picture. PVC, by code, can only be used for drain pipes, not incoming lines, due to the toxic nature of PVC plastic.
There is also a small modification to the WOM that will make your life a lot easier if you want to know how much water you have in your cisterns.
Just before the valve on the incoming line (number 1 in the WOM photo) you put another T-joint and attach a clear plastic pipe running straight up.
You want the top of this pipe to be higher than the tops of your cisterns. As your cisterns fill up, so will this clear pipe. In fact, the level of the water in the clear pipe will always show the level of the water in the cisterns, just due to the natural leveling action of water. A very simple solution to monitor how much water you have and it doesn’t involve taking the lid off your cisterns and sticking your head in it to see where the water level is at.
Obviously there are a few other components to a standard plumbing setup in a home. You’re going to have a pressure tank to make sure all of your water fixtures get water at a decent flow rate. That being said, if the pressure tank or pump ever fails, the way the cisterns are positioned to the rest of the plumbing, you will still get water just by gravity. It won’t flow as fast, but slow water is better than no water.
Additionally, you’re going to probably want some hot water. This is usually accomplished using a solar hot water heater and a gas on-demand system as a backup. The solar hot water heater is another panel that heats water from the sun instead of generating electricity. It will have a large coil of metal pipe running through it. Actually, the panel doesn’t heat the water directly. You use glycol instead because it has a much higher boiling point than water. You heat up the glycol by running it through the panel then run the pipe down to a heat exchange tank where it transfers the heat from the glycol to the water. While the sun is out, this can give you some very hot water. If you need hot water after sundown, this is where the backup system would be used. If you can adjust yourself to use the majority of your hot water during the daytime, you won’t need to use your backup system hardly at all.
Now that you have your water filtered, pressurized and heated, you can put in the rest of your plumbing to get the appropriate type of water to the appropriate fixture. This is the same standard type of plumbing that you would have in any house.
There is more to the story of water in an Earthship, but that will be covered in the section on Contained Sewage Treatment.