WATER TREATMENT & SANITATION
Potable water can be attained through either a grid-connected or off-grid system. Grid-connected systems typically utilize municipal infrastructure, while off-grid systems utilize rainwater catchment systems, wells, or springs. Likewise, water treatment (processing of grey/waste water) can be either grid-connected to main municipal sewage lines or processed through off-grid applications, requiring the use of biodegradable soaps/detergents and composting or incinerating toilets.
The diagram below describes an off-grid rainwater catchment system with the possibility of connecting to municipal water sources through a pressure-regulating inlet. The system utilizes a composting toilet with urine diverter while maintaining the option to install a conventional flush toilet. To optimize water efficiency, a propane tankless water heater is installed, and the shower utilizes one line of potable water directly connected to the water heater, which is set at the temperature desired in the shower.
Disclaimer: Water and plumbing system design is critical to occupant health and appliance upkeep. The information below is for general purposes only. You should consult a plumber and rainwater catchment system specialist for specifications that best suit your needs.
Grid-Connected Municipal Water
As municipal water is generally already treated and pressurized for standard home construction, little needs to be accommodated to access unlimited potable water for a tiny home, if connected to the grid.
Although municipal water typically comes to a home already pressurized at 40-60psi, a pressure regulator may be required to regulate the municipal water pressure in coordination with the load of the tiny home's plumbing pipes.
If a tiny home on wheels is grid-connected to municipal water, the pipes extending from the ground to connect to the tiny home plumbing system should be insulated to keep pipes from freezing and bursting in the winter. An alternative to this is to use an on-board water storage tank while pipes are winterized for a short period (see STORING section of below OFF-GRID system description.)
Off-Grid Rainwater Catchment System
The first step in the design of a rainwater catchment system should be anticipating the amount of water that will be needed to sustain a tiny home on a daily and weekly basis for all of its inhabitants. This will expand into an anticipation of how much water will be needed on a monthly and even annual basis. Calculations should include the water used by appliances (dishwasher, washer), plumbing fixtures (toilet, HVAC), water used for bathing and hygiene (shower, bathroom faucet), water used for drinking and cooking (kitchen faucet), and water used for cleaning.
The design of an off-grid tiny home should take into consideration products and methods that reduce consumption of all resources, especially water and electricity. For water, this includes products, such as low-flow shower heads and faucets; low-flow toilets or composting toilets, which eliminate the use of water entirely; a dishwasher, which cleans dishes with less water than washing by hand; and hand sanitizers, used to wash hands rather than with the use of soap and water. The reduction in water consumption can also come from lifestyle habits, such as fewer and shorter showers, considering dry shampoos and sponge bathing as alternatives; and the use of foot pumps at sinks to prevent faucets from running continuously during tasks that only require water periodically, such as when rinsing dishes or washing one's face in the morning.
The next step is to research how much monthly and annual rainfall the tiny home's geographic area usually receives. This data can be acquired on online platforms, like those of the US National Oceanic and Atmospheric Administration (NOAA) and its National Centers for Climate Information (NCEI).
Coordinating anticipated water usage with predicted monthly and annual rainfall is pivotal to understanding the feasibility of locating a tiny home geographically, and it will help predict required storage capacities and potential lifestyle habits. There are numerous online resources for sizing a rainwater catchment system, providing detailed ratios and calculations. Stephen Hren has written extensively on homepower.com outlining calculations, design, and storage of rainwater catchment systems in storage tanks above ground. And the Penn State Extension educational platform has detailed the design, construction, and treatment of rainwater catchment systems using cisterns.
In a potable rainwater catchment system, water is collected primarily from roof surfaces. This is not limited to just the primary residence, but could also include covered porch areas, sheds, etc. The more surface area, the more water.
In the collection of rainwater, the material of the surface being collected from is critical. It is strongly recommended to avoid materials with lead, as this would leach into the water. It is also recommended to avoid timber roofing materials, as the timber would absorb water and its weather treatment chemicals could leach into and contaminate the water. Exterior metal roofing is the most common material for rainwater catchment systems and is highly recommended. Slate is an alternative and safe roofing option, but for a tiny home on wheels it would be heavy and expensive.
The gutter system should bear the same material considerations in mind, and should additionally be coordinated with a series of traps that collect debris. This ensures that when water reaches the storage tanks, only small particulates of debris remain. Proper gutter sizing is critical to diverting water away from the facade, and can be sized using this calculator from METAL-ERA.
The storage of collected rainwater can be accommodated by essentially three options: on-board water tanks, off-board water tanks, or a hybrid of the two.
With on-board water storage tanks (tanks in the house), weight and space are critical issues, especially if a tiny home is on wheels. Water weighs about 8.3 lbs/gallon; if water storage is entirely on-board, it would likely cause the tiny home to exceed the weight limit of its trailer axel rating and result in an imbalanced weight distribution. Additionally, on-board water storage would be highly demanding on an already limited square footage. However, on-board storage is the most convenient means of storing and accessing water, as you do not have to worry about supply pipes freezing or having a semi-permanent housing situation in order to install an off-board storage tank.
With off-board water storage tanks (tanks nearby or underground), tanks and piping must be insulated so that they will not freeze in the winter. A typical solution to this is to place the water storage tanks underground, still potentially requiring insulated piping. This option could be limiting if a tiny home is intended to be conveniently mobile, but it is a great option if a large amount of water storage is desired. Off-board storage tanks typically come in the form of plastic or metal cisterns, but a rainwater pillow is a great option if mobility is a priority, as it could simply be emptied, rolled up, and hauled inside of the tiny home.
The final water storage option is a hybrid of both on- and off-board storage. Small storage tanks that could provide a full week of water can be placed on-board, with the primary water storage off-board, serving as a reservoir. If pipes connecting the two systems need to be winterized for a short period, water can still be accessed immediately from the on-board tank.
In order for collected rainwater to be potable, it must be filtered. Most filtration systems are coordinated for use between collection and storage, rather than between the storage tanks and its immediate use in a faucet or appliance. The latter is recommended, as it prevents treated water from sitting extensively in a storage tank before use, and ensures that water is fresh as it comes through the plumbing.
Filtration systems are typically comprised of mesh filters, calcite carbon filters, and UV filters. UV filters require constant electricity, which would tax an off-grid electric system. To eliminate the use of a UV filter, it's recommended to utilize a Doulton 3-stage filtration system, with the following filters: pre-filtration (before going through any pump, water goes through 100 mesh filter to protect pump from excess debris), sediment pre-filter, and silver/ceramic filter cartridges, yielding potable water.
In a rainwater catchment system water needs to be pressurized in order to be transferred from its storage tank through the filtration system and into plumbing pipes. This can be accomplished with water pumps and pressurizing tanks.
All wastewater in a home can be categorized under either Greywater or Blackwater. Greywater comprises most of the wastewater in any home, generated from the use of appliances and fixtures such as sinks, showers, washers, and dishwashers. Blackwater is explicitly any water that contains urine or fecal matter, such as from toilets. The below sections describe broadly how the disposal of each can be managed in an off-grid tiny home. In a grid-tied home, disposal and treatment of both greywater and blackwater is managed by municipal infrastructures.
Since greywater does not include urine or fecal matter, it could be recycled for the use of watering plants or supplying flush toilets. Depending on local codes, greywater could be channeled directly through drainage pipes to water non-edible plants. It is recommended to use natural and biodegradable soaps, shampoos, detergents, and cleaners; this will ensure that the soil and plants will not be polluted from toxicity found in bleaches and dyes.
In a grid-tied system, flush toilets (toilets with a water tank) are used for blackwater drainage. They are commonly connected to municipal sewage infrastructure, which will require permits and licensing for installation. Alternatively, off-grid systems could utilize an on-site septic system for blackwater drainage.
The most simple, inexpensive, off-grid way to manage toilet waste is through the use of a bucket filled with an aggregate, such as sawdust; this is known as a composting toilet. However, for healthier management of urine and fecal matter, composting toilets with urine diverters are recommended as they substantially reduce odor. Composting toilets could be highly productive in a homesteading environment, in which the compost could be used to fertilize non-edible plants.
Incinerating toilets incinerate urine and fecal matter rather than flushing or composting it. Like composting toilets, they are environmentally friendly and do not require water for waste disposal; however, they do require a paper liner and electricity or gas to service their incinerating function.