net zero, communal toilets, earthbag village, net-zero bathroom, water-recycling bathroom, eco-toilets, sustainable campground bathroom, green bathroom, community eco-toilet

Water Recycling Net-zero Bathroom

As part of the the open source Earthbag Village (Pod 1), we will be building and are open source project-launch blueprinting a rainwater recycling bathroom structure. We call this a “net-zero bathroom” because the water used for this bathroom will be supplied entirely by rainwater collection, so the net water use will be zero.

This page discusses the water recycling net-zero bathroom with the following sections:




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net-zero bathroom, communal bathroom, water-saving bathroom, water-recycling bathroom, water self-sufficiency bathroom, no water waste bathroom, green bathroom, eco-bathroom, sustainable design, One Community, Earthbag Village, earthbag bathroomThe Rainwater Recycling Net-zero Design (top-left in the image below) will be built twice in the South half of the village. It incorporates 100% water self-sufficiency through collection and use of rainwater for flushing and hand washing with traditional septic for county compliance. It will be combined with the Vermiculture Bathroom designs (right in the image below) and the Communal Eco-shower designs (bottom-left of the image below) to sustainably meet the complete bathroom needs for the entire Earthbag Village (Pod 1).

Vermiculture Bathroom, Eco-toilet, Net-zero Bathroom, Communal Showers

Location of Designs within the Earthbag Village – Click for the Earthbag Village Open Source Hub



net-zero bathroom, communal bathroom, water-saving bathroom, water-recycling bathroom, water self-sufficiency bathroom, no water waste bathroom, green bathroom, eco-bathroom, sustainable design, One Community, Earthbag Village, earthbag bathroomWe see the water recycling net-zero bathroom as a realistic and beneficial option for eco-communities, campgrounds, 3rd-world countries, and anywhere water resources are scarce and/or people are interested in sustainability. Open sourcing these designs as part of the Earthbag Village (Pod 1) is meant to demonstrate what is possible and provide everything needed for objective evaluation and replication.

net zero, communal toilets, earthbag village, net-zero bathroom, water-recycling bathroom, eco-toilets, sustainable campground bathroom, green bathroom, community eco-toilet

Net-zero Bathroom Features Overview Image





Alena ThompsonMechanical Engineer
Beatriz Rocha
Mechanical Engineering Student
Diogo RozadaCivil Engineering Student
Jorge Antonio RicardoMechanical Engineering Student
Matheus ManfrediniCivil Engineering Student specializing in Urban Design
Samuel Soroaster: Permaculturalist, Sustainable Builder, PhD, and founder of Green New World



Communal use rainwater recycling bathrooms will be within a short walk for all residents of the South, East and West parts of the village (see the Pod 1 layout). These bathrooms will integrate traditional septic for all toilets. The rainwater collection cistern in the center will capture and store enough water to meet all of the hand-washing and toilet-flushing needs of these bathrooms.

One Community Earthbag Village Communal Shower and Net-Zero Bathroom view looking Northeast

The One Community Earthbag Village Communal Shower and Net-Zero Bathroom | Concept Render – View Looking Northeast

One Community Earthbag Village Communal Shower and Net-Zero Bathroom view looking East

The One Community Earthbag Village Communal Shower and Net-Zero Bathroom | Concept Render – View Looking East

One Community Earthbag Village Communal Shower and Net-Zero Bathroom view looking South

The One Community Earthbag Village Communal Shower and Net-Zero Bathroom | Concept Render – View Looking South

One Community Net-Zero Bathroom Cutaway view

The One Community Earthbag Village Communal Shower and Net-Zero Bathroom | Concept Render – Cutaway View

This study by Samuel Soroaster (Permaculturalist, Sustainable Builder, PhD, and founder of Green New World) assesses the feasibility of designing a shared restroom to serve 40 uses per day with self-sufficiency of water and energy for all its demands.

  • Zero water use beyond what can be collected and stored from rain. Integration of a traditional water source to meet county requirements and guarantee function in situations of extreme drought
  • Allow us to meet county requirements with the traditional septic while we explore more sustainable models with the vermiculture and other eco-options we are open source project-launch blueprinting
  • Allow others with similar local-level restrictions to duplicate this traditional and “experimental” eco-option so we can all work together and further validate the effectiveness of these more sustainable models
  • Allow us to keep the cost of the earthbag village (Pod 1) as low as possible so it is more easily replicated

Rainwater Recycling Bathroom Design

  1. Rainwater catchment and storage.
  2. Reuse of greywater from sinks to flush toilets
  3. Water saving faucet and ultra-high efficiency toilet (UHET)
  4. Dry urinals with separate collection for males
  5. ADA compliancy
  6. Structure is made with Earthbags; foundation and water tank are made with ferrocement
  7. Roof is designed as a reverse camber (funnel) for rain catchment
  8. Blackwater is collected in a septic system that produces biogas for energy needs
  9. Hot water is heated by solar and biogas, backup is heated with natural gas
  10. Electricity is provided with PV solar
  11. Septic system is heated with biogas and natural gas for backup (still exploring this)

Fifteen inches (38cm) of average rainfall a year would be sufficient to meet the water needs of this shared bathroom design. Here are the calculations for our specific location:

  • The location receives an annual estimated 15 inches (38cm) of rain. The annual distribution of rainfall is roughly 1 inch (2.5cm) per month +/- .5 (1.25cm)
  • For 40 persons per day, an estimate of 50 gallons (190 liters) is needed to wash hands totaling in an annual need of 18,250 gallons (69.3m3)
  • With a roof of 200 sq. meters and annual rainfall of 38 cm p.a. a total of 76m3 water can be collected

Here are the catchment design specifics:

  • A first rain diverter is installed to clean roof of debris and potential pathogens of 0.5mm equating to 100liters per rainfall. Assuming 24 rainfalls per year mounting to 2m3 p.a. of water
  • Pre-filtration: The roof contains a circular flat section of 2m diameter to slow water flow to trap sediment and debris in pebbles. A fine mesh 450micron is placed to exclude debris and animals from entering the cistern. The intake is 1.5 inches (4cm) above the roof to facilitate the sedimentation process
  • All pipes to the cistern will be made of HDPE (High-density polyethylene).
  • After the water enters the 4 inch (10cm) intake it meets the first diverter. When the first diverter is full water is automatically redirected to the water tank
  • A hyperbolic nozzle maximizes oxygenation and implosion of water prior to entering the cistern
  • The cistern has a capacity of 50m3 – with a cylindrical shape of 4 x 4 m
  • Water within the cistern is recirculated for the continuous addition of oxygen though a hyperbolic nozzle
  • There shall be included a clean out valve 4 in (10cm); a 2 in (5cm) overflow valve
  • Collection of the water for use is done at 2ft (60cm) below the water surface to collect the best quality water. A buoy maintains the outflow at a consistent depth.
  • The water tank shall be built with a superadobe wall 12in (30cm) of 200PSI. The interior of the cistern shall be made with ferrocement 1000PSI of 3 in (7.5cm) with a 1/4in (0.6cm) welded steel lattice. (Needs engineer verification to meet code)
  • Since rain has a tendency to be acidic, pH of water tank will be checked on a monthly basis and adjusted with dolomite lime to a pH of 7.6 – 8.0
proposed rainwater catchment plans, One Community

Plumbing Design Described Above with Additional Details Below


Here are the plumbing details:

  • All pipes from between the cistern to the pressure tank shall be ¾ inch galvanized steel
  • All pipes after the pressure tank to toilet faucets will be ¼ inch copper TYPE L
  • Filtration/Disinfection: Water from the cistern is filtered through a 3-stage filter consisting of a  200 micron pre-filter, a 0.5 micron fine filter and a GAC filter. Disinfection is performed with an inline ozonator. Alternatively, code permitting, ionization with silver and copper is performed
  • After filtration a ½ HP pump will pressurize a 50 Gallon pressure tank to 20 PSI
  • Plumbing is separated at the pressure tank to run one line to the hot water system while the other line runs to the sinks of the toilets
  • Sinks are equipped with 1 GPM faucets that have motion sensors.
  • Toilets are of UHET norm with a dual flush feature of 0.5 and 0.8 gallons (1.9 and 3.4 liters) per flush

The hot water system will also be built with self-contained sustainability in mind:

  • Hot water lines runs from the pressure tank to the roof where a radiant solar panel will heat the water.
  • Secondary hot water with NG/biogas on demand water heater.
  • The distance to the most remote sink is 8 m @ 1/4in pipe has a water retention of 0.6 Gallons (2.5 liters).

Greywater will be used to flush the ultra-high-efficiency toilets:

  • A 5 gallon chamber underneath the sink will store the greywater from the sink
  • The chamber is equipped with a micro-ozonator or UV light to disinfect the greywater
  • The chamber has 3 lines connected: overflow, secondary inlet, outlet to toilet chamber
  • Secondary inlet is connected to float valve when water level drops below one gallon a gallon of potable  water is added
  • Microfloat switch in toilet tank is activated when toilet is flushed to fill toilet tank
  • Small 1/16 HP 1 GPM pump will be used to fill toilet tank
  • Alternative to an overflow a second float switch can activate the pump if water is too full in the greywater chamber
  • Dry urinals will be placed in all toilets except the ADA toilet
  • 1.5inch plumbing will serve to run all urinals to a collection chamber that will be used for fertilizer production (to be determined)

Here are the sewage system design details:

  • Assumption for UHET daily usage: 40 uses for fecal matter per day with 0.9 gallon per flush, 80 uses for urinal with 0.5 gallons for females. Total flush volume 36 gallons and 40 gallons
  • All sewage lines shall be of the HDPE 4 inch type
  • A dual chamber septic tanks shall be installed connected to a leachfield
  • Sewage lines shall be vented and equipped with a p-trap prior to the septic tank
  • The hydraulic retention (HRT) shall be at least 30 days for the septic tank.

Calculations for septic anaerobic digestion system:

  • 40 daily stool deposits at 400g average per visit resulting in a daily amount of 16kg of feces.
    • Human Feces: Total solids (TS) of 25% and volatile solids (VS) 85% of TS with an average N of 5% and C:N ratio of 8.
    • Every gram of VS provides 0.9 liters of biogas

Objective to maximize biogas production:

  • C:N 30:1
  • 10 % final w/v Total Solids
  • Total Solids of 2.5g per liter per day
  • Hydraulic retention of 40 days

Volume and density septic tank calculations

  • 40 flushes  x 3.4 l H20 per flush + 0.4 l feces  = 152 l per day of slurry = 40 G
  • 0.4kg feces / (3.4 liters + 0.4 liters) = 0.105 = 10.5% (w/v) slurry
  • 400g x 40 /2.5g TS per liter per day = 6,400 liters volume needed = 1680 G
  • 1680 slurry volume x 1.1 gas space = 1848 Gallon Septic Tank Volume
  • 6,400 liters / 152 liters   = 42 days HRT

Nutrient balance calculations

  • 400g x 0.25 TS x 40 =  4000 g = 4 kg of TS per day
  • 4000 x 0.05  N = 200 g of N per day
  • 200g x 8 C:N =  1600 g of C provided
  • 200g x 30 C:N = 6000 g of C required per day
  • 6000 g – 1400 g = 4600 g of additional C needed per day

As recycled or unbleached toilet paper is mostly cellulose it can be assumed that every toilet user will utilize 15 g of toilet paper which is 100% C x 40 persons results in 600 g of C per day.

Compensation can be achieved with sawdust: C:N 400 with N 0.1%

  • 1000 g x 0.001 N x 400 C:N  =  every kg of sawdust provides 400 g of C
  • 4600 g C need – 600g Toilet paper  =  4000g needed of C per day
  • 4000 g / 400 g = 10 kg of sawdust added every day will optimize the C : N ratio – in other words, 287 g of sawdust added per person providing feces

Energy calculations:

For Human feces:

  • 40 persons  x  400 g  x  0.25  x  0.85= 3400 g of Volatile Solids per day
  • 3400 g x 0.9 l biogas/g VS = 3060 liters biogas = 3.06 m3 = 110 FT3 Biogas produced per day
  • Assuming the biogas will be 70% CH4 with CH4 @ 1060 BTU/ FT3
  • 110FT3 x 1060 BTU/FT3 x  0.7  =  81,620 BTU per day from feces of 40 people

For Sawdust:

  • Calculations coming

Here are the energy consumption calculations for each of these bathroom domes:

  • Conversion of gas to electricity is 3,412 BTU per 1 kWh with engine efficiency of 35%
  • 16 light LED light bulbs 3 watts each running 6 hrs = 0.3kWh
  • Greywater pumps 0.05 kWh running 2 hrs = 0.1kWh
  • Pressure pump 20PSI, 80 Gallons, 0.5kWh running 2hr = 1kWh CHECK
  • Electric total is 0.3 + 0.1 + 1 = 1.4 kWh
  • Electricity generation is 1.4 kWh / 0.35 efficiency x 3412 BTU/kWh = 13,648 BTU per day
  • On demand water heater 45,000 BTU per hr = 45,000 BTU per day
  • 81,620 BTU generated – 45,000 BTU – 13,648 BTU = 22,972 BTU remaining to heat digester.
  • Heating demands to maintain digester at 90F needs to be determined


The total area of the bathroom below is 58 m². Each bathroom has the area of approximately 4.6m². The water storage is located on the center of the structure and has an area of 12.5 m² and a volume of 44 m³. The rainwater collected on the storage will be used for flushing the toilets and washing hands. The idea is to wash hands with filtered rainwater and recycle the water to flush toilets.

To check the rules for the ADA compliant bathroom this guide was used. The dimensions are shown below.

figure 3

The dimensions of the toilet, sink and door are illustrated in centimeters here:

figure 4figure 5figure 6

To simplify the visualization of the bathroom, the software Revit (version 2014) was utilized to create the 3D drawings. Some views are shown below.

figure 7

Figure 7- Top View bathroom, Revit

figure 8

Figure 8- Section Box, Revit


figure 10

Figure 10 – Section 1, Revit

figure 11


Figure 11- Section 2 and components dimensions, Revit

figure 12

Figure 12- Section 3, Revit

figure 13

Figure 13- Elevation East, Revit





net-zero bathroom, communal bathroom, water-saving bathroom, water-recycling bathroom, water self-sufficiency bathroom, no water waste bathroom, green bathroom, eco-bathroom, sustainable design, One Community, Earthbag Village, earthbag bathroomA rainwater recycling communal bathroom structure has the potential for broad application in communities, campgrounds, 3rd world countries, and anywhere else water resources are scarce and/or people are interested in sustainability. Housing and sustainable showers and solid waste processing can be added to these designs with the Earthbag Village (Pod 1) and its Vermiculture Bathroom designs and Communal Eco-shower designs.



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