Off the Grid: Tiny House Rainwater Collection

Many people join the Tiny Living Movement because they are interested in saving money and/or the environment. Going off the grid is one way that you can help your pocketbook and the planet at the same time. But how “off the grid” can you really be in a tiny house? One of our biggest needs in everyday life is water. We use is for drinking, washing clothes and dishes, and for showering. Rainwater collection in off-grid systems is one way to feed your supply.  It can also allow you to keep your expenses down and even reduce your carbon footprint.

We sat down with Jim Harrington, owner and designer of the Rain Water Pillow to get some of the facts that you need to know about rainwater collection when you are taking your tiny house off the grid.

Realistic Expectations

The catchment area of a tiny house alone is probably not large enough to provide enough water for all of its occupants year round. However, as Jim says, “If you asked me for 10 dollars and I only offered you three, would you not take the three dollars?” Rainwater collection may not fully replace your consumption unless you live in an area with higher than average rainfall, but it can certainly augment your plan and save you some serious money.

Doing Some Math: Supply vs. Demand

To determine how much water you can harvest, use the following formula from the Tiny House Design and Construction Guide:

Off the Grid - Rainfall Collection - chart 2

This formula should be calculated for each month, since average rainfall will vary from month to month. The US Climate Data can give you an idea of how much rainfall you will have where you live. Now let’s figure out how much you are typically going to need? When calculating the amount of water you will need, be sure to consider all or your activities that use water. Below are a few of the common activities and their typical consumption. Again, from the THD&CG:

Off the Grid - Rainfall Collection - chart 1

Assuming your usage is 15 gallons per day and the dimensions of your tiny house are 8 feet by 24 feet, then you would require approximately 4 inches of rainfall each month. Depending where you live, you may or may not have enough to get by. Jim also talks about how not all parts of the country are created equal. “If you live in California and you get all of your supply in three months, you will need a large cistern to hold your water,” Jim explains, “If you are in an area like on the east coast, the rain may fall a little more evenly so you are able to go with something smaller.”

Off the Grid Does Not Mean Dirty

“One of the biggest concerns that people have is about animal droppings in their rainwater catch,” Jim says. “But if you look at where most cities’ water comes from, it is lakes and reservoirs. Think about how much ‘stuff’ there is in storm water runoff alone, never mind all of the animals, fish, and even humans that are in that water, and you will quickly realize that roof water is incredibly clean.”

Jim’s water solution has three levels of filters as well as a pass through UV light and a charcoal block before the water is drinkable. The truth is that the cities of the world need WAY too much volume of water to do that kind of a filtering to your water at home.

Storing the Water

Off the Grid - Rainwater Collection - PillowSo most systems require you to have a tank somewhere and in the colder environments, you have to definitely keep that tank indoors so that it doesn’t freeze. The Rain Pillow can be made to fit any space and it is portable as well. So if you need it to fit under your bed, a kitchen cabinet, or you have enough room to put it outside, you can have it custom made to fit. If you want quick disconnects on it so that you can take it with you, consider it done.

In Conclusion

While rainwater catchment in a tiny house is possible, you will want to make sure you have a backup or supplemental water source. And know that all water is not forever. Jim will tell you, “Droughts happen and wells dry up. Be prepared by valuing your water and understanding your consumption.” For more information on the Rainwater Pillow, click here.

Do you plan on going off the grid? What fears do you have? let us know in the comments below.

13 thoughts on “Off the Grid: Tiny House Rainwater Collection

  1. CathyAnn said:

    Excellent article and links! Thank you!!!

  2. Carrie Chisholm said:

    I saw on TV’s Tiny House they used an outdoor cistern, I think it ran 2-4000$. When how and why would this be applicable?

    • Dan Louche said:

      You definitely want to be able to store more than you will need in a given time, otherwise you won’t be able to survive the dry spells.

  3. Christine Ferguson said:

    Such practical help is so appreciated. Thank you C. Ferguson Spain

  4. Alan Churchill said:

    I live in a rainforest – in the rainy season I can harvest 2200 gallons a month from my tiny house roof. Thanks for the formula.

  5. brandon said:

    another option is to re-filter your greywater through the system and use a composting toilet. closed loop system means infinite water!

    • Dan Louche said:

      I’ve talked to a few people about this and they say it’s not very practical. Grey water gets very oily and quickly clogs and destroys filters. I’m sure there is a way, but it’s not as straight forward as it sounds.

      • Michael Schneider said:

        Use a living biological filter. An example is the water hyacinth in the deep south. Disney uses in the canals to pretreat wastewater before recycling it. On a much reduced scale aquariums do the same.

  6. Kathy said:

    There’s also your roofing material to consider. Water does pick up trace amounts of metals from metal roofing. I’d be ok using it for showering but not for drinking/cooking. But then I always use a water filter that removes pesticides, chemicals, heavy metals and fluoride (none of which we need anyway!).

  7. mjr said:

    One of the first things about renewable/off grid utilities is to reduce demand. Ultra low flow fixtures can take the shower and sink down to 1/2 gpm. I mix my Dr. Bonner’s soap with water in the soap dispenser. That way you only need to run the water when rinsing.

  8. brian irving said:

    How can you find out more info on the pillow when their web site hosting has been cancelled?
    Brian Irving
    CozyHomes Tiny Houses Australia

  9. Kris said:

    How long can rainwater be stored and still be safe to use? Is it possible for mold, algae, or other things to grow within the water storage container?

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