How to Capture and Store Enough Rainwater for Your Cabin

One of the most important resources you need to be able to enjoy your cabin is water.

Obviously, you can bring water with you to your cabin if you don’t have any other options.  While water is necessary to survival, not having a good water source at your cabin isn’t a deal breaker.  But, it can have a huge impact on your level of comfort and enjoyment at your cabin.

We’ve talked on Cabin Freedom about various ways to get water at your cabin.  Today, I want to dive in a little deeper on rainwater.  I’ll help you figure out just how much rainwater you can capture and store at your cabin, what things you need for a good rainwater collection system, how to store rainwater for use at your cabin, and how to clean it for potable use.

How much rainwater can you capture at your cabin?

The very first question you need to ask before designing and building a rainwater collection system, is can I capture enough rainwater at my cabin to justify such a system?

If you don’t get very much rain at your cabin, then a large rainwater collection system wouldn’t be prudent.  You should probably just stick with a single rainwater collection barrel and system like I talked about in this article.

But if you get lots of rain at your cabin, then a rainwater system may be able to provide you with all the water you need for your cabin.

How much rain do you get at your cabin?

So here we go.  How much rain do you actually get at your cabin?

The easiest way to find out is with a simple Google search.  Just google “average annual precipitation in ______” and fill in the name if the closest town to your cabin.

I found that where my cabin is, we get about 25 inches of rain per year and 75 inches of snowfall.  I’m actually going to mostly ignore the snowfall component mostly because snow is much less dense than rain, and I don’t really care how many gallons of snow I could capture.  I’m only interested in how much water I capture.  If I get 100 inches of snow, that’s probably somewhere between 20 and 50 inches of actual water.  So to stay conservative in my estimate, I’ll say that the snow is 20% as dense as the water so my 75 inches of snowfall is more like 15 inches of rain.

So I’m getting about 40 inches of water per year falling at my cabin.

How much rainwater actually lands on your cabin roof?

Now, to figure out how much rainwater I can actually capture, I need to figure out how much rain actually lands on the roof of my cabin.

If you have gutters on all the low points on the roof of your cabin, you can capture most of the water that lands on your roof.  So let’s figure out how much water that actually is.

Start by determining the square footage of your roof.  The slope of the roof doesn’t come into play in this calculation.  We want to know the square footage of the footprint of your roof.  If your cabin is rectangular, then this is just the length of your cabin multiplied by the width.

If your cabin is 20 feet wide by 30 feet long then it’s 600 square feet.  If your roof overhangs a little then you can add that on.  I’ll just use the 600 square feet number to keep it simple.

Now, we need to convert the amount of rainfall from inches to feet.  We said 40 inches in the example above.  So we’ll take 40 inches and divide that by 12 (because there are 12 inches in a foot).  That’s 3 1/3 feet of water.

Now, to get water volume we’ll multiply the square footage of the roof by the amount of rainfall.  That’s 600 square feet times 3 1/3 feet of water.  That’s 2,000 cubic feet of water per year.  Multiply cubic feet by 7.48 to get gallons.

So at this example 600 square foot cabin that gets 40 inches of water per year, a total of almost 15,000 gallons of water land on the roof per year.

But how much do you need?  Well, if you have flushing toilets, a normal shower, and you wash your clothes just like most people in first world countries, then you use 80-100 gallons of water per day.  So the 15,000 gallons at this cabin will last one person less than half a year.  However, if the owner of this example cabin conserves water and only uses the cabin on the weekends, then this cabin could collect enough rainwater to run everything for the year.

Going through these numbers can help you figure out if a rainwater collection system is worthwhile and if you’ll need to supplement it with something else, like capturing water from a stream or hauling some up to the cabin with you.

How effectively can you capture the rain at your cabin?

The next question is can you actually capture all 15,000 gallons of rainwater?

There are a few things that will impact your ability to do so.

  1. What are the precipitation patterns in your area?  Does all the snow melt and the rain fall in a matter of about 3 months?  If so, then you’ll need a lot of storage to be able to utilize all 15,000 gallons in the example above.  On the other hand, if it rains an average of 1-2 days per week almost year round at your cabin, then you’ll be able to capture plenty of water with fairly minimal storage.
  2. How much water storage is feasible at your cabin?  A lot of people use the 275 gallon water totes I wrote about in this article.  Others are using 50-gallon drums.  Whichever you use, how much storage can you actually keep at your cabin?  Now, this number could go up substantially if you install an underground water tank.  You can get an underground tank anywhere from 1,000 up to over 3,000 gallons for storing water at your cabin.  But for most DIY types, a couple of 275 gallon water totes above the ground is all they’re going to want to or be able to use for rainwater collection.  That may limit you to only about 500 gallons of rainwater storage at your cabin.
  3. How much can your system handle?  We’ve seen rainstorms where the gutters just can’t keep up with the rain and the water starts pouring over the edges.  Likewise, the piping from the gutters to the water storage need to be able to handle the volume of water that falls in these rainstorms.  If the piping can’t keep up, you won’t be able to capture all of the rainwater.  Now, that’s okay if you get enough rain or have enough surface area that you get plenty of water at your cabin.  But for those of us on more desert climates, the system needs to be able to keep up whenever the rain falls.

You can see that just because you get enough rain at your cabin, doesn’t mean that you’ll be able to capture and use it all.

What are the elements of a good rainwater collection system?

Now that we have determined if a rainwater collection system is a good idea for our cabin or not, let’s look at what elements make for a good rainwater collection system.

The following four things are important for high-quality and high capacity rainwater collection at your cabin.

Early Filtration

The best place for filtering out large particles is right at the beginning.

The easiest way to capture rainwater from your cabin roof is via gutters.  And the best place to start filtering that water is at the gutters.

A simple gutter cover from any home improvement store will do the trick.  These covers or screens are intended to keep leaves and other stuff out of your gutters so they stay cleaner.  But they’ll also filter a lot of the gravel from your roof and other debris.  That way the water going into your system contains as little debris as possible.

You can also install a screen at the point where the water goes from your gutter into your storage system.  This will help catch other debris that makes it through the gutter covers.

First Flush System

The next thing you should include in your cabin rainwater collection system is a first flush system.

What this does is give the first water that flows over your roof a place to go other than your storage containers.  That way anything that makes it past the early screens will get flushed out of your system before going to the water storage containers.

This will keep things like bird poop, dust, and other finer particles from getting into your stored water supply.

To see how I would recommend setting up a first flush system, keep reading.  There’s a link to a YouTube video at the end.

Storage

Obviously a system like this will require storage.  But the amount of storage you need will depend on your situation.

If you need 5,000 gallons of storage, doing something underground makes the most sense.  But if it rains fairly regularly year-round at your cabin, then 500 to 1,000 gallons will be sufficient and you can store that above ground in water totes.

You also need to have these storage containers all piped together such that the water flows through the containers and out at some point to go into your cabin or wherever you’ll use it.  Again, the video will show you how to do that.

Overflow

Having an overflow on your water storage is also important.  If your water tanks fill up and it’s still raining, then without an overflow system the water will just flow over the edge of your gutters.

It’s better to be able to decide where that water will go.  So out the top of your storage system, you should have a water pipe that’s below the level of the gutters and will carry any excess water to wherever you want it to pour out on the ground.  This can be just a few feet away from your cabin.  You just don’t want the water pouring over the gutter and pooling right next to your cabin walls.

How do you store rainwater to use at your cabin?

Now we know most of what we need to capture and store rainwater to use at our cabin.  But how do we safely store it so it won’t get all full of algae?

When water sits stationary, it tends to grow algae.  This makes your water taste bad and could make it unsafe to drink.  Plus, as algae builds up it can gum up your system.

Here are the two best solutions to that problem.

Make Your Storage Tank an Opaque Color

Algae grows through the process of photosynthesis, like other plants.  So in order to feed and thrive it requires sunlight.

One of the best ways to prevent algae from building up at all in your water tanks is to make them an opaque color.  By that I mean that you should paint or cover them with something the prevents as much light as possible from getting through.

The video below will show you this step.

Add Chlorine or Bleach to your Stored Water

I also recommend that you treat your water so kill any algae or bacteria.  To do this, I recommend that you open the top to the uppermost storage tank in your system and add a small amount of bleach to the tank.

You can actually just use basic household bleach (5.25% to 8% sodium hypochlorite) as long as it’s unscented and doesn’t have any other soaps, cleaners, or color-safe products.  Use no more than 1 teaspoon for every gallon of water in the tank.  A full 275 gallon tank will take about 5 3/4 cups (sources: University of Florida and EPA.gov).  I would pour in just enough to treat one tank-worth of water.  As it flows through your system, it will help eliminate any algae build-up in your system.

I would also just do this on an as-needed basis.  If your water starts to have discoloration or an odd flavor to it, treat it.

If your bleach is not 5.25% sodium hypochlorite, I suggest you go to the EPA website link above to see a table indicating the right amount of bleach to use based on the concentration of your bleach.

How do you clean the rainwater for potable use?

For the water coming out of your rainwater system and into your cabin, I recommend a whole-house filter.  However, I wouldn’t necessarily worry about filtering water that’s going to be used for cleaning.  I would, however, filter water that will be used for drinking and dish washing.

Installing a small reverse-osmosis system under your sink might actually be sufficient.  Or else, you can forego the filter and use a counter-top filter for drinking water only.

If you want more information about cleaning the water at your cabin, no matter where it comes from, you can read my article on the subject here.  You’ll learn all about my favorite counter-top filter for cleaning drinking water.

Check out this great video guide to building a rainwater collection system for your cabin or home

I would go into great detail on planning and building a rainwater collection system.  But there’s a guy with a great YouTube tutorial on building one of these.  This is a 7-part video series on planning and building a rainwater collection system. Check it all out here.

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