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Rainwater Catchment

Auerhaus is the first approved rainwater system in Clatsop County. All the water I use comes off the roof. I was planning a rainwater system, but I was forced to make it a primary source after drilling 227 feet and finding only a gallon a minute of blue mud. I was naive. I thought if you moved to the country, you dug a well. And in Oregon how could there not be water? When my well came up dry locals asked, "who witched it?" When I replied, "I'm a man of science, I don't believe in witching or dowsing for water," they just shook their heads in sad disbelief. My neighbor Hank even loaned me his copper rods that had found water on his property. And I had to admit I did feel them cross and not where we drilled.

I came to understand that well drillers are really hole drillers. Later, when others would say, "we're gettin' a well drilled," I would remind them, "no, you are getting a hole drilled. With luck you will get water." There was a certain amount of irony in drilling for water in the fall of 2003 at the start of the rainy season. It is the height of human folly to put a straw into the ground and blindly search for water at the same time soft, clean water is falling on your head.

>Rain V. Well

Rainwater Pros

  • Naturally clean
  • Naturally soft
  • Dependable (works from storage tanks of known volume)
  • Requires lower cost, lower power pumps.
  • No certified water source needed before building permit issued.
  • Can gravity flow in an outage if storage located above point of use.
  • May be a source of water for fire fighting.
  • Unregulated by Oregon Water Resources Department


  • Requires a metal roof
  • Limited to amount in storage in dry months. Requires planning.
  • Mineral-free water (except maybe zinc if galvanized is used).
  • Gutters need to be cleaned depending on location.
  • Plumbers may not be familiar with how to design or install it.

Well Pros

  • Volume if one finds a very high volume, dependable source.
  • Needs no above-ground storage or structures.
  • Source of minerals.


  • Expensive to drill (and uncertain)
  • Expensive to maintain
  • Expensive to operate
  • May require power far from home site.
  • Need to prove volume and potability before getting a building permit.
  • Susceptible to contamination
  • Can be an entry point for aquifer contamination
  • May require filtering, and softening
  • May dry up
  • Requires generator backup for flow in a power outage.
  • Restrictions on location
  • Regulated

>Calculating Storage Needs

A good rule of thumb is that one inch of rainfall on a 1,000-square-foot roof produces 600 gallons of water. My 800 square foot roof produces about 45,000 gallons from our 60 to 80 inch annual rainfall. In winter I don't need any storage, but in summer, when we can get no rain at all, I need at least 90 days worth. How much is this? According to testimony before the U.S. House Committee on Transportation and Infrastructure, May 20, 2003

The typical residential household uses about 50-85 gallons of water per day for drinking and cooking, bathing and showering, flushing toilets, and washing dishes and laundry.

For the average family of 2.5 people that is 2.5 x 85 gal/day x 90 days = 19,000 gallons. I have 1/6th that in storage. How did I justify this?

The minimum standard for wells in Oregon is 225 gallons per day. However, this is considered sufficient for up to 3 households. Thus I argued 35 gallons/day for a small, cabin-like house should be sufficient. In fact, I only use 10 gallons per day, and 3000 gallons turns out to be almost a one-year supply! However, I have no dishwasher, I do laundry in town and it has been suggested by some that I should shower more often. What people don't realize is that I'm using 3-times as much water as I used in the manufactured home I lived in during construction. It had only running water to the kitchen sink from a 55-gallon barrel I refilled by hand from a county spring.

Here's the Excel spreadsheet I created to determine how much storage I needed. auerhaus_rainwater.xls


It's hard to find good, practical information on rainwater systems. Here's what I know.

My roof and gutters are stainless steel. Not as much of an extravagance as one might think in the grand scheme of things. Painted metal or galvanized work just fine too. One drawback, stainless can be blinding in the sun. The gutter is a standard half-round shape, but the downspout was custom formed.

In my system the water is collected off the roof into a 300-gallon holding tank. This provides the initial filtering by settling. It's good to have the tank outdoors because its easier to clean, and I wasn't really eager to route 50,000 gallons of water directly through the basement.

I had to customize my tank in two ways. First I added a 3" through-tank fitting on top to receive the gutter flow. Second I installed two float sensors on the tank, one at the top and one just above the outlet. I got these at Grainger. The through fittings can be found at farm supply and pipe supply shops. The sensors are needed to use with a pump controller so the pump operates to pump down the whole tank and doesn't cycle on and off with each small rainfall.

I also neglected to run 1 or 2 pair of control wire from the storage tanks. That's because I thought I would pump all the water uphill and just dump any excess there. But because I use so little I don't really need to run the pump that often. Being able detect if the upper tanks were full would be a nice improvement.

I did remember to leave 3 holes in the foundation: line in from the holding tank, line up to the main storage, and line down from storage. I didn't remember to leave another hole for the sensor wire, but a Bosch hammer drill took care of that.

Pumps & Filters


The water from the holding tank runs into the house through a 4" x 10", 10-micron filter (A). This is important to protect the pump and to keep the storage tanks clean. I bought my filters and sterilizer from Ohio Pure Water Company.

Next a Dankoff Solar Slow-pump (B), factory wired for 110V AC instead of 12V DC, is used to pump water up to storage. The Dankoff, though expensive, was used for its low power, slow pump rate. (And on DC, one of the few pumps that can be connected directly to a solar panel with no charge controller.)

I couldn't find a plug-and-play controller so I built one based on the Levelite controller (C). I liked this approach because the sensors that go in the tank are low voltage. I wasn't comfortable with immersed 110V pump switches. Installing them would have also meant having to run a protected electrical circuit outside.

The return path from storage involves 3 more parts before it is hooked in and ready to drink. First stop another filter. Same 4" x 10" housing, but I think I've got a 1-micron filter in it (D). This ensures there will be no particles that could hide anything from the UV light. Also, the filter protects the pressure pump, a Grundfos MQ pressure boosting pump with integral pressure tank (E). This is a very nice product that adds 45 psi to whatever is coming in. In my case maybe a pound or two. I was mistakenly shipped the 220V model, but 110V is available and would have allowed me to run it off of the solar/battery side. But at 750-watts I wasn't sure I could afford it in a power outage. Now I think I might. Instead I have a bypass valve that allows gravity flow in an outage.

Finally the Trojan UV Max (F) I chose this for several reasons. First, it's whole house, rated at 9 gallons/minute. The model I chose meets NSF/ANSI 55 Class A UV. No need for chlorine with an expensive dosing pump, chemicals, and post-treatment charcoal filtering. Soft, clear rainwater is the perfect match for UV sterilization. Hard water and turbidity are the biggest challenges for UV effectiveness. At 75-watts continuous power, it does draw 54kwh a month (about $6/mo). The bulbs aren't cheap ($100) and need replacing every 15-months. And obviously this works best with an uninterrupted power supply (around $15k).

Storage Tanks

The main storage tanks were reasonable (about 50¢/gallon), but proved hard to get. Because they are large and light they are expensive to ship. Different sizes and shapes are made in different regions of the country. I wanted three 1-thousand gallon tanks; I ended up with 2 @ 1350. I learned, after having to reject one order, that it is best to buy what is made in your area.

I also didn't really think through how the tanks would be plumbed, and I plan to re-plumb them. Maybe if I'd gotten the three 1000-gallons tanks I might have been able to move them to clean them, but in fact it's not really practical, and anything bigger than 300-gallons should just be plumbed with regular pipe. I used RV, potable water hose for flexibility, and this will be replaced largely with fixed pipe.

The other improvement will be to pump into only one tank and let the overflow go into the second tank. And then to put valves in to draw out of only one tank. This is so a leak in one won't drain both and so one at a time can be emptied for cleaning.