How to Build a Rain Harvest Water System

[dranderson71]

The Intro

I love the idea of a green section in this forum. I'm going to focus on how to build a rain harvest water system and break it up over a couple of posts given the amount of content. This is a true life build, I implemented it at my house almost 2 years ago and it is working without issue to this day. And you can do it to with basic handy man skills. Not only can it help the environment it can save money.

Rain Harvesting is capturing rainfall on a catchment surface (normally a roof but possibly even a driveway) for either potable or non-potable usage. This approach is used heavily in many developing countries and is catching on in the southern / southwestern states in the U.S. that are now realizing there is not as much cheap water as there once was. California is
the state you hear about the most in the news right now.

The simplest implementation of this system (non-potable) provides a cheap, replenishable water source for such function as drinking water for livestock or for watering a lawn / garden. In this instance the basic requirement is simply a catchment surface, a storage means (cistern, runoff pond, etc), and a movement mechanism for the water (gravity if you're lucky, water pump if otherwise). Many of my friends living in the suburbs complain about the cost of watering their yards, being charged an excessive amount to pull the water from the tap and then a second charge for that same water going back into the sewer. With a minimal of investment, this cost can be significantly reduced / eliminated.

The more complex implementation, and the one I will focus on, is a potable water source solution. The non-potable solution only requires a subset of the potable one, so by walking through the potable covers the non-potable by default. The solution at my house provides all the water needs for my house, both potable and non-potable, and is the cleanest water I've ever had.

If the environment and money aren't good enough reasons, consider these as well.
- Softness: You don't need a water softner, afterall its rainwater and as soft as it gets. I wash my car and don't have to deal with spotting anymore, guests comment on how nice showers feel, etc.
- Chemicals: Public tap water is cleaned and filtered at processing plants prior to consumption, but they are having significant issues removing the traces of prescription drug residue from that water. Pills people ingest get into the bloodstream, get filtered by the kidneys, and find their way back into the water supply. And prescription drug usage is extremely popular in the U.S., from depression to diet to sexual enhancement. You may be drinking someone else's medicine cabinet...


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[dranderson71]

When starting an initial design, it's good to consider all of the following before moving too far ahead. In some environments a rain harvest system may not make much sense, in others it may be too costly for a full solution. Here are some things to think about.

1) How much water do you / your family need daily?
This should include whatever you intend to use it for: drinking, bathing, washing clothes / dishes, watering the lawn / garden, etc. Remember that your pets drink too, don't forget about them. There are a number of calculators on the net to help you determine the avg consumption in gallons per day based on your specific usage needs.

2) How much rainfall does your area receive?
If you get regular rainfall, your storage capacity can be smaller. Not much rain? You need more capacity to make it through the dry spells. There are websites that post the average rainfall around the country, be sure to find one with decades of data. That's right, I said decades. If you want a solution that will get you through the best and worst times, you need to know decades worth of rain data. A little forward planning here saves tons of headaches later. It's worth it.

3) What is your catchment surface and how much of it is available?
A steel roof has a high runoff coefficient (the percentage of water the surface can actually capture vs being lost) than a asphalt shingle one and makes for a more efficient water capture surface. A large barn roof can capture more water in a short rainfall than the roof on a small garage.

4) How do you want to store your water?
Some housing communities may require your cisterns to be out of sight or underground, this may influence your decision. Ponds are often the cheapest storage, but are difficult to keep clean and normally require more acreage than people have. Plastic tanks are cheap and light but require replacement within 10-20 years depending on their environment (buried, exposed to the sun, protected, etc). Ferrocrete / Concrete last the longest by far, but are not easily relocated and tend to be more costly.

5) How many 'outages' are acceptable over 10 years? Over 40?
Water can always be trucked in, but it's expensive to do so. Size the system too small and gains made in cost are lost to paying the water trucks. Oversize it and you may have a system that cost you a lot but never runs out of water.


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[dranderson71]

And now, the nitty gritty of making this happen. First, some background on my scenario. I live in rural NC nowhere close to public water which left me drilling a well. The only issue was the well contained ferrous iron content that constantly stained my pipes / toilets / showers and fouled my pumps. I then dropped a couple grand and 3-4 years on a Kinetico water system that, while reducing the issue, never completely removed it. After these years of frustration, and without many other options, I started looking into rain harvesting. Now I will say this. I overbuilt my system intentionally, I didn't want to have to rely on water from anywhere else ever again, and I was willing to pay more to ensure that. And in hindsight, if I would have done this right from the beginning and skipped the well drilling (couple grand easy) and the Kinetico system (another couple grand) I would have effectively paid for this system right from the gate. And now my maintenance is almost nil, I don't have to buy chemicals or the like anymore, and my water is the cleaner than most bottled water (most bottled water comes from municipal taps - believe that?). Here's how I did it.

The below relates to a document and spreadsheet that I put together for these details / calculations, but I'll need an admins help to get that posted unfortunately - or pm me and I'll email it to you):

1) How much water do you / your family need daily?
My family consists of me and my wife only. we're not large water users and have no garden or lawn to consider. We did, however, want the system to provide the potable and non-potable needs for the entire house. Using the calculators I found on the net I calc'd this to be 31 gallons pp / day or 62 gallons needed per day for my house.

2) How much rainfall does your area receive?
Using meteorological data on the internet I was able to pump in 57 years worth of rainfall data into my spreadsheet for the calculations. The more data the better.

3) What is your catchment surface and how much of it is available?
I had about 1400sq ft of asphalt shingles readily available and another 250sq ft to incorporate in later if need be. Some sites say you shouldn't use asphalt shingles as catchment, but you can - you just have to seal them properly.

4) How do you want to store your water?
I chose 3 plastic tanks. They were relatively cheap, I can replace / fix them readily in the future (I have no concrete / ferrocrete skills), and they would fit in a protected area under my deck.

5) How many 'outages' are acceptable over 10 years? Over 40?
I sized mine for 2 outages in 50 years. More than enough for what I need.


Taking this information I then plugged them into my spreadsheet. I know knew:
1) How much water I needed monthly (demand)
2) How much rainfall I would receive monthly (supply)

Using the spreadsheet (again, pm me and I can email it) and based on the number of outages I deemed acceptable I could then determine my storage capacity needs. In my case this came out to 4800 gallons of capacity, which I then split into 3 1600 gallon cisterns. Why 3? Size, cost, redundancy. A smaller size would fit under my back deck. Once you get over 2000 gallon cisterns they cost more to make and ship. And lastly if one failed I still had two that could supply my house until the broken one was fixed.

And now that I knew the capacity, I was ready to design the rest of the system.


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[dranderson71]

Again, my document has pictures that will make this easier to understand, but I'll try to explain it here as best I can.

Here is the general 'flow' from rainfall to usage in the house:
1) Rainfall captured on roof catchment surface (sealed asphalt shingles)
2) Gutter screens filter out large debris like leaves and twigs
3) Standard 4" PWC piping delivers the rain toward the cisterns
4) All water goes through a WISY fine filter for additional sediment removal. This is for the most part a self-cleaning filter that uses induction to pull the water through mesh screens leaving the sediment to be washed out an exhaust pipe
5) Water enters the system through a baffle / calmed inlet (to minimize water disruption) and into Cistern 1. Here the water initially settles.
6) Cistern 1 is connected inline to Cistern 2. Here the water settles further.
7) Cistern 2 is connected inline to Cistern 3. Here the water settles further.
8) A floating suction filter draws water from Cistern 3. This approach is used as the 'best water' is the aerated water towards the top of the tank but 6" under the surface.
9) Pump draws water from the cistern and pushes it into the pressure tank.
10) Water flows through a 3 micron paper filter for anything that has gotten past the other filters.
11) Water flows through a UV filter which kills any bacteria that may exist.
12) Water is used by the house!

Again, I oversized it for limited outages and honestly went overboard on the filtering (it's rain water to begin with, I really don't need all that additional filtration) and the oversized UV filter was almost $1000 by itself. If your needs don't require this, you can build a cheaper and just as effective solution.


And I'll say it one last time, the docs I have explain this better in pictures and contain the links to the products that I purchased in building this. It better rounds out the explanations above and I'll be happy to email it to anyone who asks (it took me a LONG time to pull all this together, so PLEASE, if you reference it / reuse it at least give me the credit. I don't ask for compensation, just some credit is all ).

Hope this helps those that are interested in building their own rain harvest system. Best of luck in your project!
Darin

[alia176]

Wow, what an excellent article. There was a LOT of hard work, trials and tribulation went into that project.

Thanks for sharing.

[wingrider78]

Can you please mention where you found your decades worth of data??? I have your spreadsheet and I couldn't find it in there either...

[dranderson71]

Originally Posted by wingrider78

Can you please mention where you found your decades worth of data??? I have your spreadsheet and I couldn't find it in there either...

To the first question, where can you find historical rainfall data. You have a couple of options, and can get both on the internet.
1) Buy it: Don't know if URLS allowed, so I'll spell it out. www dot Weather dash Warehouse dot com. This wasn't available when I started my research, and it looks like you can buy your rainfall data there. The more you want, the more you pay. This would be easy but more expensive, needless to say I didn't use this.
2) Find it: And this will take some good old investigative digging. Do searches for 'Historical Rainfall Data' or consult the state department of climatology website. Airports keep this data for many many years and are great sources. For NC and my area for example, I found mine here (again spelled out) www dot sercc dot com. At the site from the menu choose 'Climate Data' -> 'Historical Climate Summaries'. On the next page I chose my state, then the closest airport location to me. Lastly on the related page, scroll down the left pane and choose 'Monthly Precipitation Listings' -> 'Monthly Totals'. So not straightforward as easy, but with a bit of fortitude it's free and that works for me.


In regards to where its on the spreadsheet, remember there are multiple tabs:
1) Sheet Documenation : Explains the columns and usage
2) Monthly : Main sheet for testing and calculating your water needs
3) Yearly Data : This contains the historical rainfall data. Note that mine goes from 1949 - 2006.

Hope that helps. Everything I needed for this rain harvest water system I researched on the internet, the information is there but sometimes it requires some 'creative' digging Best of Luck!

[wingrider78]

Yes, I found all the data on the "yearly data" tab, but I was saying that I couldn't find WHERE you found all that data mentioned in your file you emailed. Thank you for pointing us in the right direction...

[Gunguy45]

Just a note to people that may read this later...

It can be illegal in some states/areas to retain rainwater runoff without a permit and verification of the intended use....yes, crazy sounding I know. But many areas are fed by underground aquifers that are replenished mostly by rainfall.

CO, AZ and a few others have regulations on these systems.

[AnthonyJP]

Wow, I have to say it's very cool of you to make your home a green home by using rainwater. And thank you very much for sharing what is evidently years of hard work on your part. I want to make an investment like this soon... because I know the returns will be great, as well as the savings.

I have taken a bath using rainwater and it really feels great on the skin... smooth and refreshing, and it takes away the roughness.