Urban Survivalists

In each of our projects we plan to do a fairly detailed design processes so that you can see just how we are coming to our design conclusions and how they can be modified to fit your own circumstances. To that end, we will give you all the relevant equations so you can do the calculations yourself and walk through our reasoning for involved designs. That isn’t to say we won’t be making use of materials on hand or lucky circumstances. We will. What it does mean is that you will get a reason for all of our decisions. If you don’t, give us a holler and we’ll make the reasons known.

Disclaimer:

We are going to attempt to create a large rainwater harvesting system for our home. This system is temporary and mobile, so it does not apply to Portland city regulations. In most cities, harvested rain water can only be used for irrigation.  You must check with your city laws to determine if this is the case for you.  It is not, under any circumstances, legal or safe to connect a harvested rain water collection system to a municipal water system.  This is because a contaminant could be brought into the city water through the rain water harvesting system and endanger other peoples’ lives.  Please check with local government agencies before using water for other uses than irrigation. It is also common to only allow collection of water from roof tops, so if you are planning collection from somewhere else, it will probably need to be checked out.

In our area, rainfall is heavy enough to justify quite a bit of work in order to collect rainwater to offset our current water usage. We plan to achieve this by modifying our current gutters to route the water into barrels for temporary storage. Sounds ambitious but it is really very easy and requires mostly off-the-shelf components and a little bit of ingenuity. Our biggest concern is keeping this project so that a renter–like ourselves–will be able to do it and not freak their landlord out. Generally this means modular/movable systems that can be taken out to restore the house to pre-project conditions without cutting or otherwise modifying the house.

Below is a Google Sketchup picture of what a possible rain barrel setup might look like. Now with this basic idea in mind, we will begin to ask some fairly simple but important questions.

House image provided by Dilbert
A user by the name of Dilbert uploaded it into Google’s 3D Warehouse and then we modified it to add the barrels and such. As an aside, yes, we know the pipes connecting the barrels should be on the bottom of the barrels if they are all going to be able to empty from the spigot. We just got tired of drawing before we noticed our mistake.

Roof Area

How much water will we potentially collect?

Gathering data for your area concerning rainfall is an important step in the design process. You need to know how much water you are likely to collect so that you can determine the size and number of storage containers needed. Most importantly, this means not having too many barrels. If you live in Arizona or the Gobi dessert, you won’t need 10 barrels.  Also, for future builds, we will want to know how much water we are going to need to filter on a daily basis. Gathering this data cannot be a haphazard step in the design process because so many future decisions will depend on it. Be sure to write down your data and keep it in a safe place. Sometimes projects can take a long time to complete and loosing your hard earned data is not something you will feel pleased about.

For our area we were able to find the relevant data in Wikipedia. The rainfall averages 42.7 inches (1,080 mm) per year in downtown Portland. Portland averages 155 days with measurable precipitation per year.  This gives us 42.7/12 ft or 3.6 ft of rain per year. The next piece of information we need is the square footage of roof where we live. Most often, this is the same as the square footage of living space, unless the home has multiple stories. We are renting a 1500 ft^2 home, so 1500*(3.6) = 5337.5 cubic ft of water that we have the possibility of collecting per year. Typing “5337.5 ft^3 to gallons” into the Google search bar will return our results without the hassle of knowing the conversion factor (7.48 gal per ft^3). So 5337.5ft^3 = 39,923.0 gallons per year. This is how much we can expect to collect if we were able to collect all the water from our roof.

These calculations do not take into account any evaporation of water from the roof, although there are reduction factors for this.

On a daily basis, we can expect to collect ((Yearly Rainfall)/(Days of Measurable Precipitation)/12)*7.48 gallons of water. For us, that comes out to 257.6 gals. Now, that seems like quite a lot and it is. However, we aren’t going to be able to collect that right off and it assumes we are collecting every drop of water from our entire roof. Also, we are only averaging the yearly rainfall over the number of days with measurable precipitation. The reality of the situation is that on some days we are only gonna get a millimeter or two of rain and on others we are going to get a whole inch.

For starters, we are only going to collect water from the back of the house at a single downspout. We estimate that the area of roof that flows into this downspout is about one third the total roof area.  This is about 500 square feet. If that is the case, then our potential collected water per day is equal to 257.6/3 = 85.9 gallon per rain day. This is much more reasonable for our test barrel of 65 gallons.

Gutter Configuration

Do you replace old gutters?

While we were checking out our gutters, we noticed that they were made out of wood. This means that they are really, really old! Below you can see some images of our antiquated gutters. We have decided to replace these because attaching fittings would not be very easy with the wood gutters. Also, vinyl gutters are not very expensive. Not to mention, keeping a new gutter clean of debris is much easier than keeping an old gutter clean.

“This is the total length of gutter to be replaced. The half closest to the camera is wood, while the half farthest away is made of metal.”

“Image of the gutter outlet underside. This was taken just after the snow storm, thus the ice. You will notice that this gutter is made of wood.”

“Top view of the gutter outlet. As you can see, it has accumulated a lot of moss. This is another reason for the replacement.”

Now that we have decided that we will be replacing our existing gutter, we needed to decide how we will be keeping the new gutter clean once it has been installed. Also, you should get permission from your landlord before replacing something like a gutter. Chances are they won’t mind but you should check first. We did!

Cleaning out gutters and preventing debris accumulation

There are a number of different methods to keeping your collected rain water clean from debris accumulation. We intend to cover our gutters with a mesh to prevent leaves from getting in. In addition, we plan on creating a roof wash system with two parts. The first part is a tube that will collect the first wash of water from our roof, a first-flush system. The second part is a sand filter known as a roof washer. Since we want really clean water to be coming out of our rain barrels, we wanted both systems even though it is fairly effective with just one if you are only using the water for irrigation. It is necessary to have at least one system because roofs can become fairly dirty between rain events causing disease.

We will be using a 1/2″ mesh for covering our guttes. The mesh is vinyl and water safe. Avoid aluminum or other metal gutter guards as you can pick up contaminants from them that you will only have to filter out later. In general, you want to cover the entire upper opening of a gutter system so that all large debri will be kept out. Inside of this outer grating and directly on top of the downspout opening, you will want to install a smaller gratting to take out finer debris. Ours will be a piece of standard vinyl mesquito screen. We purposfully went for vinyl again over the more common metal stuff for the previously mentioned reasons.

“This is an image of the gutter guard vinyl mesh that we purchased to protect our new gutter system.”

That is all for this week. next week we will talk about first flush systems roof washers and barrel inlet and outflow. If you want to read up on some more rain water harvesting information, check out our Links and Resources page.

P&S