Tiny House Water Systems – Part 1

This is the second post delving into the various systems in a tiny house. For the others, please see the links at the bottom of the introductory post, here. Note that I originally planned to have this one post encompass water supply systems, water heating systems, water waste systems and winterization concerns; however the post ended up being so long that I decided to break it up into two posts: Part 1: covering water supply and water heating systems Part 2: covering water waste systems and winterization concerns which will publish on schedule this Friday.

“Water, water, every where, Nor any drop to drink.” Samuel Taylor Coleridge, The Rime of the Ancient Mariner

Water is a necessity of life, but providing for it in a tiny house can be challenging. The options range from hooking up to utility provided water, to collecting and filtering rainwater on-site, to lugging it all in from elsewhere in jugs / barrels / goatskins / buckets / coolers / canteens / etc…

Jug of water over pan
Jug of water over pan

The simplest solution is to have a jug of water with a spigot over a catch basin.  Simple, to the point, limited only by the amount of water you are willing to haul in (in jug-full increments). Heating is external to the system (unless you put the jug in the sun), and coldness depends on the ambient temperature (or liberal applications of ice). Dirty water is thrown out on the ground, just don’t throw the baby out with it!

Mickey as the Sorcerer's Apprentice hauling buckets of water
Hauling water is hard, just ask Mickey!

Of course, there are downfalls to this system, namely heating the water can be problematic, there is a limited supply, and hauling it all gets tiresome after a while. In many countries, the tap water is not considered safe to drink, and you have to buy water at the store in 5 or 10 liter containers. In some cases, a home will have a cistern, and pay to have a company send a water truck out to refill the cistern on a regular basis.

Water Supply

Aside from carrying water in from off-site, there are many options available on-site, depending upon the locale. These range from a clear mountain stream, to a well, to rain water cistern, to a municipal water system. All have advantages and drawbacks to be considered.

a crisp drink from, a mountain stream
a crisp drink from a stream

If you are lucky to be distant from civilization, you may have the luck of having access to a nearby stream with clean water. Now, although it may look crystal clear and perfectly harmless, there are potential risks involved that I would prefer you hear from others more learned than I about. I neither advocate for nor against drinking straight from a stream, it is merely an option to be considered. In the event that you have determined that the water is safe to drink, there exists the need to bring the water to your tiny house in a usable fashion. This can be done either using gravity or via a pump. Both require similar equipment, although gravity fed requires larger pipes and a source that is a fair elevation above your tiny house. Here are specifics on how  to set up a pump version, the gravity fed system will be similar, but it also is an article all of its own on how to set it up (that I have not found a neat little link to like the above yet,) so it may be a future article here. Water Well t Water Well types Another option is a well. As you can see above, there are a number of different types. The dug well is the traditional version from antiquity. Typically dug through the use of hand tools or with a backhoe today, a dug well is still common in many parts of the world. The well is dug down to below the water table, continuing to dig until the water coming into the well exceeds the rate at which the digger(s) can bail the water out of the hole.

Dug stone well, with cover and windlass to lift water bucket
Dug stone well, with cover and windlass to lift water bucket

To prevent sidewall collapse, a lining of stone, brick, tile, or other material was installed. Some sort of protection was built at the entrance to protect from items falling into the well, including runoff from rain. As shown in the illustration to the right, for most European cultures there is typically a windlass with a bucket attached with which to draw up the water.  Dug wells have their drawbacks, in that they rely on the water table remaining at a level that allows water to be removed from the well. This water table naturally fluctuates with the amount of rainfall a region gets, and it is not unusual for a well to dry up in times of drought. Dug wells also have the drawback of being really easy to contaminate. The water table that these wells tap into is the sub-surface water, which collects all of the contaminants  that are washed into streams and percolates into the ground. This includes pesticides, fecal mater, dead and decomposing animals, oil, trash, etc. Nowadays, the most typical type of well is dug using a drilling rig similar to that used in drilling for oil. They typically bore a 6 inch hole 100-400 feet into the bedrock, intersecting fractures in the rock that carry water. By law, at a minimum the top 18 feet of the bore must be cased with either a plastic or metal sleeve. Once the well is drilled, a submersible pump is lowered into the well, which pumps the water up to the surface.

A modern well, showing the pressure tank. Note that the well pump is actually  a submersible style at the bottom of the well bore, shown to the right in the picture.
A modern well, showing the pressure tank. Note that the well pump is actually a submersible style at the bottom of the well bore, shown to the right in the picture.

In most homeowner type installations, there is a pressure tank at the surface that is maintained at a certain pressure by the pump which provides the water pressure in the pipes in the home. In colder climates, this a well house (not shown) is built around the well and pressure tank to provide protection from the weather as well as providing an enclosure that can be heated to keep the above ground pipes and tank from freezing. The pipes are run to the house underground, typically by trenching down to below the frost line in the area (6 inches to 6 feet, depending on how close to the poles you are) and then back filling the trench once the waterline is installed. As the power that runs the well is typically supplied from the house, it is not uncommon for the power line to be placed in the trench as well, either within a conduit or using a type of wire that is rated to be buried underground.

A typical rainwater  harvesting set up
A typical rainwater harvesting set up

Rainwater Harvesting is another historical option. Does your tiny house have a metal roof? Do you have space to place a cistern (tank) in which to store the captured water? Then you may be able to harvest rainwater to supply your tiny house. Calculating the amount of water you can harvest in a year is simple: Maximum Annual Gallons of Rain Capture = Annual Rainfall x Square Footage of Roof x .623 Gallons If you are curious why you multiply by .623, that is how many gallons are in an area of one square foot by one inch deep of rainwater For instance, an 8 foot by 16 foot tiny house has a conservative minimum roof surface of 128 square feet. In Huntsville AL (where RidgeRunner Tiny House is located) the annual average rainfall is 54.34 inches. so using the above equation: Annual Rainfall: 54.34 x Square Footage of Roof: 128 x .623 Gallons = 4,333.29 gallons maximum annual gallons of rain capture. But this is what you would capture in an ideal world. Depending upon the type of roof you use, some water is lost due to evaporation or absorption. The typical rainwater capture efficiencies for roofing materials are as follows:

  • For a tile or metal roof, use a 95% efficiency factor
  • For a concrete or asphalt roof, use a 92% efficiency factor
  • For a bare soil roof, use a 75% efficiency factor
  • For a gravel roof, use a 70% efficiency factor
  • For a grass roof, use a 17% efficiency factor

So, if our hypothetical 8 x 16 tiny house example above uses a metal roof, it would actually be able to capture 4,116.62 gallons a year. However, before you rush to install a rainwater harvesting system for your tiny house, you need to realize that in a typical household, a typical person will use an average of 50-100 gallons of water per DAY. This may seem high, but if you take a bath or a typical shower, the gallons quickly add up. This means that even if you are so efficient that you use 20% less than the lowest typical person (40 gallons a day) a entire year’s worth of water in Alabama captured from the roof of our example tiny house would only last one person approximately 103 days, less than 1/3rd of a year. So unless you have a shed that is over twice as big as your tiny house that you can use to supplement your supply, you will need to consider other options (unless you live in a rain forest). Also, you need to realize that there may be regulations concerning water harvesting in your area. In some parts of the Western US, it is actually ILLEGAL to harvest rainwater on your own land. No, seriously! Specifically, it is still against state laws to harvest rainwater from a roof in Colorado. At the opposite end of the spectrum, Australia actually mandates that water harvesting is implemented for any remodeling or new construction in most Australian states. If you want more information on rainwater harvesting, I recommend Harvest h2o.com for doing further research. The final option is to hook up to utility/municipal water supplies.  There is a cost involved, but unlike most of the other options above, the utility company is responsible for not only ensuring the reliability of the water supply to your tiny house, they are responsible for ensuring the safety of the water being supplied.

Hot Water Systems

Although a bracing cold water shower is an invigorating way to wake up in the mornings, very few of us enjoy that sort of shock to our system. In fact, I would be willing to say that that majority of us prefer to take hot (or at least warm) showers and baths, even in the dog days of summer. Humans have figured out many ways over the years of heating water. These range from a pot over a fire, to a kettle on a stove, to a tank style hot water heater, to a solar hot water panel, the lost goes on and on. i will touch on a few that people tend to consider when deciding how to heat water in their tiny houses.

Heating water over a campfire
Heating water over a campfire

The most primitive is a pot heated over a fire. Just like with the jug of water above, this is the simplest method, but not necessarily the easiest. You are limited in the amount of water heated at one time by the capacity of the pot, and the time it takes to heat the water is limited by the amount of heat from the fire that is captured by the pot. There is also the matter of keeping the fire lit, and hot enough to heat the water in a short amount of time.  There is also the drawback of weather and environment having an effect on the ability to heat he water efficiently. Is it windy? Then the fire’s heat may be blown away from the pot, resulting in long heat times. Is it raining? The coolness of rain counteracts the heat building in the water, not to mention potentially putting out the fire, removing the source of heat. You can always bring the heat source indoors, heating water on a stove using a pot or kettle.

ZODI Outback Gear Fire Coil Water Heater (Note, linked item does NOT come with water containers)
ZODI Outback Gear Fire Coil Water Heater (Note, linked item does NOT come with water containers, despite the somewhat misleading initial list of features be sure to read the last line of the description)

There are campfire heaters that are designed to capture the heat in the embers of a campfire and automatically channel it from a cold container to a hot water storage container. These are more efficient than a pot over a fire, and they do work well, but they still have the inherent drawback of relying on a campfire for heat, as well as being limited to the water volume in the supply jug. True, you can hook up a larger hot water jug and switch out supply jugs as they empty, or even hook the supply side up to your well water or utility water, But ultimately you are limited by the either the heating capacity of the fire, the storage capacity after the water is heated, or by the amount of water available to be heated. As you have probably figured out, to have usable hot water, you need four items:

  • A supply of water to be heated.
  • A source of heat
  • A means to transfer heat from the source to the water
  • A means to store the heated water

We touch upon the supply of water to be heated in the first section of this post. The source of heat can be a fire, the sun, a stove, a heating element, or a gas flame. We have touched on a camp fire as a heat source above. The transfer of heat typically occurs by means of a container being heated and transferring heat to the water. The storage of heated water is typically a tank, preferably insulated, and sized based on the inverse of how quickly the water can be heated. The Fire Coil water heater shown above makes it easy to see the basics of heating water. The water is fed at a slow rate to the source of heat in a container that allows the heat to be transferred, in this case the copper coil. You may think that if you increase the size of the copper tubing that you would increase the rate of hot water generation, but that is actually incorrect. The small size of pipe actually ensures that the water moves slowly enough that it has time to heat up while in the “heating zone”. If you increased the size of pipe, more water would move through and at a faster rate of speed, which would actually mean each molecule of water would spend less time in the heating zone and therefore would end up not being as hot in the end. As you can see, there is a bit more to the science of  creating a well performing water heating system. So let’s delve into some of the other options that have been engineered to work well, starting with the standard style electric hot water tank.

Diagrams of Electric and Gas Tank Style Water Heaters
Diagrams of Electric and Gas Tank Style Water Heaters

A standard tank style hot water heater consists of an insulated tank and one or more heating elements that are immersed in the water. For an electric heater, these are resistance elements, ie. elements that heat up when electricity is run through them due to the resistance of the material to the flow of electricity.  Depending upon the size of the tank, there may be 1, 2, or even 3 elements within the tank. For gas heaters, there is a burner at the bottom which heats up the bottom of the water reservoir, then the hot exhaust gases flow up through the center of the tank, further transmitting heat as they pass through the tank, before heading up a chimney to the outside. Obviously, the size is dependent upon the amount of hot water that is needed, and the means used to estimate that amount is dependent upon the type of hot water system you wish to install. This page from the Department of Energy explains how to estimate the size of the hot water heater you need by technology, but I will briefly recap the technique used for tank style.

Sample Energy Guide Label for a Hot Water Heater
Sample Energy Guide Label for a Hot Water Heater

Look for the water heater’s First Hour Rating. The first hour rating is the number of gallons of hot water the heater can supply per hour (starting with a tank full of hot water). The Energy Guide Label lists the first hour rating in the top left corner as “Capacity (first hour rating).” For the example shown to the left, it is 57 Gallons. You then need to estimate the peak hour demand that your tiny house will have. Peak Hour Demand is defined as the maximum demand in any one hour. Ie, determine what time of day (morning, noon, evening) you use the most hot water in your home. Keep in mind the number of people living in your home. Then using the chart shown below, add up the actual number of gallons that are used within that hour to estimate your maximum usage of hot water during this one hour of the day.

  • Shower: 10 gallons avg.
  • Shaving (0.5 gallons per minute): 2 gallons avg.
  • Hand Dishwashing or Food Preparation (2 gallons per minute): 4 gallons avg.
  • Automatic Dishwasher: 6 gallons avg.
  • Clothes Washer: 7 gallons avg.
Reliance 6 20 SOMS K 20 Gallon Compact Electric Water Heater

So as an example, if your maximum use within 1 hour is 2 showers plus hand washing of dishes, the calculation would look like this:  2 x 10 gallons(showers) + 1 x 4 gallons (dish washing) = 24 gallons. Once you know this First Hour Demand, you will want to match your hot water heater’s rating to the demand. Too little, and you will run out of water before you are finished, too much and you are wasting energy keeping water hot. For future reference, the 6 gallon water heaters commonly referred to as point-of-use heaters, have a typical First Hour Rating of 8 gallons.  For the hypothetical example above, you will most likely need a 20 gallon tank style heater. These take up to 24 x 24 x 26 inches worth of space, and weigh up to 230 pounds (the water alone is 162 pounds of that) when full.

How a Tankless Heater works
How a Tankless Heater works

For tiny houses, many people look to use a tankless style water heater. These work by flash heating the water as it passes through the unit. They choose them because they take up less space than a tank style, and weigh less since you are not storing a tank full of water. They are available in either electric or gas fired types. Both electric and gas work, but the gas fired types tend to be more efficient to operate. However, the gas versions require both intake air and a chimney/exhaust. Tankless water heaters are rated by the maximum temperature rise possible at a given flow rate. Therefore, to size a demand water heater, you need to determine the flow rate and the temperature rise you’ll need for its application. First, list the number of hot water devices you expect to use at any one time. Then, add up their flow rates (gallons per minute). This is the desired flow rate you’ll want for the demand water heater. For example, let’s say you expect to simultaneously run a hot water faucet with a flow rate of 0.75 gallons (2.84 liters) per minute and a shower head with a flow rate of 2.5 gallons (9.46 liters) per minute. The flow rate through the demand water heater would need to be at least 3.25 gallons (12.3 liters) per minute. To determine temperature rise, subtract the incoming water temperature from the desired output temperature. Unless you know otherwise, assume that the incoming water temperature is 50ºF (10ºC). For most uses, you’ll want your water heated to 120ºF (49ºC). In this example, you’d need a demand water heater that produces a temperature rise of 70ºF (39ºC) for most uses. For dishwashers without internal heaters and other such applications, you might want your water heated at 140ºF (60ºC). In that case, you’ll need a temperature rise of 90ºF (50ºC).

Ecotemp L10 High Capacity Outdoor Tankless LP Water Heater
Ecotemp L10 High Capacity Outdoor Tankless LP Water Heater

So for our example house, we will assume that we will wash dishes by hand, and have at most a shower and the sink faucet running at the same time. Our hypothetical sink faucet has a flow rate of 2.2 Gallons Per minute (GPM) and our hypothetical shower head has a rate of 2.5 GPM. This adds up to a maximum of 4.7 GPM. We are not needing to heat water for a dishwasher, so we can get by with a 70ºF (39ºC) temperature rise. Or we can decree that the house rule is that if someone is taking a shower, no washing dishes! This will drop our required flow rate to just the 2.5 GPM. Which means a tankless heater similar to the one to the right should suffice. Note that the one shown is designed to be mounted outside of the house. This allows you to avoid having to run a chimney through your envelope, and avoid having to worry about whether it is getting enough airflow. It also frees up space inside, since it is mounted outside. Of concern to tiny house users is that many tankless manufacturers state that their units are for use in a standard house, and that using them in a mobile application like an RV (or tiny house) will void the warranty, so read the warranty restrictions prior to purchasing. This is due to the internal elements not being designed to withstand a lot of vibration or bouncing, which could cause some of the units to get knocked out of adjustment when travelling.

Atwood XT 6 Gallon RV Water Heater
Atwood XT 6 Gallon RV Water Heater

As always, the RV world has options available that may work for your tiny home. Specifically, a number of the RV water heater manufacturers have come up with a hybrid tank/tankless solution, that uses the operational concept of a providing a flow rate with having a small storage tank which effectively increases the available flow rate for a certain BTU output. These heaters are also compact, designed to fit into the spaces that traditional RV water heaters take up. A good version to consider is the Atwood XT line of water heaters. Like all RV water heaters, it is designed to be mounted into an exterior wall, as it exhausts to the outside through the cover (not shown). Some other options available for tiny homes are various types of solar hot water heaters, but those will have to wait for another post. Friday, I will post Part 2 – Waste Water Systems, Winterization, and Other Water Related Issues.

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