Currently the majority of tiny homes are built to accept pressurized water hookup from a hose. Simple, but also quite limiting if the house is ever moved for a few days (or longer) to somewhere where there is no pressurized water hookup- a music festival, or, say, a vacant alley lot. Standard micro houses also require water for toilets, and then a sewage hookup to dispose of it- most inconvenient, and always a little gross.
So, for not much more $, the Minim house has a rainwater collection systems, and on-board water that that can be filled up and remain off any water connection for up to a week at a time. One can do this either by a) building houses with elevated water tanks and gravity fed water, or b) building tiny homes with RV-like tanks and water systems. In the latter case, we can also design the system to allow hook ups to pressurized water if/when that is available. The essential components of this modified RV system include:
- 40 gallon RV fresh water tank (available in many sizes from places such as thetank-depot). This should ideally be mounted within the building envelope (insulated area) to keep water from freezing- as should all piping. If this is not possible, there are a variety of electric RV water tank heaters available. It should also be mounted securely, as it will weigh over 320 lbs when full.
- A greywater tank to store used shower and sink water.
- A fresh water fill inlet to fill up the tank (unpressurized)
- A fresh water fill inlet to fill run the system without the water tank (i.e. when pressurized water is available)
- A water pump (we’re using this standard SHURflo 2088-422-444 2.8 Classic Series Potable Water Pump). Note that this is a pump designed to run off of 12 volts, but you can easily substitute a 120 VAC model.
- An accumulator tank to reduce pump cycling and smooth water flow (such as this SHURflo 182-200 Pre-Pressurized Accumulator Tank)
- A simple water strainer to pre-filter the water (such as the SHURflo 255-313 Classic Series Twist-On Strainer 1/2″ FPT x 1/2″)
- Some one-way valves to allow city water to plug into the system without any manual switching of valves.
- A hot water heater. This can be a) a traditional small electric heater, such as the 2.5-10 gal Aristons (highly recommended), b) RV-specific (and pricey) tankless water heaters such as the PrecisionTemp RV-500, or c) residential tankless heaters such as the wall-mounted Eccotemp FVI-12-LP (note that this also requires 120 VAC to run).
Design: The system can be plumbed according to a traditional RV schematic, below, with a few caveats:
- No blackwater tank: at Boneyard Studios we’re using Incinolet incinerator toilets, which just uses an electric connection to dispose of waste. So we don’t plan to have any water going to the toilet (and consequently no toilet plumbing, no blackwater to dispose of, and no blackwater tank to take up valuable space).
- No hot/cold water mixing for shower. Almost all small water heaters have temperature settings on them which obviates the need for a separate cold mixing valve- simply lining in the hot water directly to the shower is simpler and works great, just adjust the temp at the tank. Also note that one may run an electric water heater for 5-10 minutes prior to a shower, and leave the heater off the remaining time (this is quite efficient, and allows one to run an electric water heater in an off-grid electrical system, such is done in Minim House).
When plumbing the system, consider designing to to be a) easy to drain, for when the house sits empty during winter, and b) keep pipes outside of the walls, tastefully exposed, so if they fail, they do not fail disastrously, and can be more easily repaired should any freezing ever rupture them.
Water Efficiency: water efficiency becomes much more important when not connected to pressurized water. This Bricor 1 gpm low-flow model is one of the most water efficient showerheads one we’ve found (there is even a .55 gpm model, but at a rate less than .96 gpm, the tankless water heater does not click on- a widely noted tradeoff of tankless water heaters- always check minimum flow rates). Bricor will even ‘tune’ the showerhead to match the water pressure your pump generates (in this case, 45 psi). Bricor also seems to make the most water efficient faucet aerator on the market (.375 gpm). At this rate, a 40 gallon fresh water tank would give 30 minutes of shower + 26.6 minutes of sink time. It’s worth noting that this water efficiency is far superior to any RV on the market today, as they all use flush toilets and typically less efficient showerheads/aerators. Also note that one of the most water saving devices we’ve come across are the foot pedal water valves, available at restaurant supply stores. These valves are incredibly convenient, more sanitary, and much more water efficient than standard faucets- highly recommended.
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