Here are some highlights of the Earthship system for catching water, reusing water, and treating waste water.
Amazingly, Earthships in Taos, which gets only 8 inches of rain, are able to supply all their water needs from water collected from the roof. This is accomplished through a well designed catchment system, water conservation, and water reuse.
The typical water use per person in
the US is about 80 gallons per day, the Earthship is designed to drop that use
per day down to 20 gallons. With this lower water usage, even
Earthships in low rainfall areas are able to capture sufficient water from the
roof to be self sufficient. Water usage is reduced by using grey water for
toilet flushing, low flow shower heads, low water use washing machines, hand
dish washing, and by not using water for an evaporative cooler (which is not
Earthships also contain a simple mini sewage treatment plant. The Earthship does not export sewage to a sewer system or put sewage into the ground.
To me, this water management system is the Earthships most impressive feature. The fact that this can all be accomplished with simple designs that you can build yourself makes it all the more amazing.
The Michael Reynolds book "Water From the Sky" covers the entire system in quite a bit of detail, and is well worth the read even if you don't plan to build an Earthship -- many of the concepts and designs will work in other types of residences. You can get the book from Earthship central: www.EarthShip.com
The water system has three main components:
The water catch (roof, cistern, and water filtering)
The grey water treatment and reuse system
The black water treatment system
Here are brief descriptions and some pictures of each of these system to whet your appetite. The book mentioned above provides descriptions of these systems that are sufficiently complete to build from.
The Earthship roofs are carefully designed to catch every drop of rain that falls on them. The rainwater from the roof if collected in one or more cisterns. The cistern is usually an integral part of the Earthship.
The roofs are designed with water collection in mind -- in a nutshell this means:
Shaping the roof to collect water
Using roof materials that can collect water cleanly
High capacity water collection troughs or gutters that route the water to the cistern
Filtering out junk in the water so it does not get in the cistern
Keeping all the parts from freezing
Orienting the roof so that snow does not evaporate before it gets collected
One message here is that an efficient roof/cistern water catching system should be a part of the design from the start. You can probably catch some water from any roof, but to catch clean water efficiently calls for a roof that is designed for that purpose.
Typically the Taos Earthship roofs have low sloping roofs that face south. The lower slope allows for better collection and doesn't let your valuable snow slide off the roof. The south facing roof slopes ensure that the snow melts and gets collected before it evaporates. The south facing arrangement also reduces freezing problems.
The Earthship crew have tried a number of roof types -- here are the ones that can work:
Metal roofing -- long life, clean water, but impossible to form into curves.
Cement Plaster coated with Acrylic coating -- any shape you want, but the plaster cracks and the Acrylic coating require maintenance.
EPDM -- good roof and clean collection, but requires professional installation
Brai with Acrylic coating -- adapts to shapes, good clean collection with Acrylic coating
The book goes into much detail on the pros/cons of each type.
The Hut Earthship uses the Cement Plaster coated with Acrylic coating. Here are some pictures of the Hut roof and cistern:
The Hut roof looking East -- one of the two roof domes min foreground, and trough leading to cistern area. Dirt slope to the right is the north wall berm.
Hut Roof -- The trough leading to cistern. The upslope to the left is the south side roof kickup for the window wall, and one of the two roof domes is in the right foreground. The wood lid on the cistern is visible, and the gravel filters out debris before the water enters the vertical tube through small holes that are below the gravel surface. This type of debris filter is somewhat self cleaning, as the wind tends to blow away loose debris.
Hut Roof -- looking up the collection trough to the East (away from the cistern). Note the small repairs in the Acrylic coating. The two main roof domes are to the left (North). The tank for the thermosyphon water heater and the batter storage compartment for the PV system batteries are on the seen on the East end of roof. Two of the openable sky vents are also visible. The sky vent in the foreground is over the kitchen area. The sky vents are counterweighted by the rock weights at the end of the 2X4 arms. The sky vent is held down by a cleated rope from the inside, and opens under the influence of the counterweight when the rope is released.
Looking at the cistern from the ground with one of the roof domes in the background -- from the SW.
The cistern lid. Note the small holes in the vertical tube where the water enters the cistern. The proximity to lots of cistern water at about 40F keeps this from freezing in the winter.
The cisterns catches and stores water for later use. Water is pumped from the cistern when needed.
The cisterns are arranged such that water can flow off the roof by gravity to the cistern inlet, and so that cistern outlet can gravity feed the pump inlet. Basically, this means the top of the cistern needs to be at or below the roof level, and the bottom of the cistern should be at or above the Earthship floor level.
Typically the cisterns are earth bermed and integrated with the Earthship structure, which keeps them from freezing.
The inlet to the cistern includes a debris filter to keep junk from getting into the cistern -- see picture above.
For the Earthships, cisterns are normally either plastic tanks, or cement plaster tire walls with an Acrylic coating. The use of galvanized tanks is not recommended because the eventually rust.
Water Distribution System:
The water distribution system for the Earthships consists of:
A 12Volt Dc pump that draws water from the cistern
A set of filters that filter the water before it is used in the Earthship
A pressure tank that fed by the pump, and supplies pressurized water to the Earthship faucets and appliances.
A solar water heater that heats water bound for the hot water faucets.
A backup water heater -- normally a tankless (demand) gas heater.
All of the pump and filter components are typically mounted on a board like the one pictured below. These can be supplied by the Earthship crew, which simplifies the plumbing.
The "WOM" -- Water Organizing Module. Cistern water enters at left and goes through the 60 mesh filter before arriving at the pump inlet. The pump outlet goes to a 500 mesh filter. At this point water for the kitchen sink and shower is taken off. Drinking water goes through the last two filters to special faucets in the kitchen and bathroom for drinking water.
The 12 volt DC pump is a Shurflo, and looks similar to the type used on RV's. The pump turns on when the pressure tank pressure gets down to about 20 psi, and turns off when the pressure tank gets up to about 50 psi.
The pump is located as low as possible in order to keep its prime from the cistern.
The WOM can be purchased as a completely plumbed module from Earthship central.
The odd looking pipe loop in the foreground is because the solar water heater had been bypassed for some reason.