Rainwater Collection

Martin Arhelger, one of our former Board members, has a rainwater collection system installed at his home and never dug a well.   Martin has developed a rainwater collection page for your information and to offer a forum for homeowners to ask questions and get answers from our neighbors who use rainwater collection either in total or to supplement other well systems.


Why collect rainwater:

1.       Good – really good water.  What Richard Heinichen, of Tank Town, calls “fresh squeezed cloud juice.”  There’s no need for a softener, no clogged shower heads, no water heaters filling up with lime, no spotted dishes from the dishwasher, no need to add any chemicals to your water, no need for reverse osmosis (which wastes a lot of water) before water is drinkable.

2.       If your pump goes out, it’s right there to on the surface, not near the bottom of your well.

3.       You can gets tax breaks and rebates, both local and Federal.

4.       You don’t need to worry if the water table drops since you’re not drawing from it.

5.       It’s better for your plants.

6.       Oh, and it’s really good, really safe water.

In an article in the City of Austin Water Utilities Conservation Program publication, “Wastewater Newsletter” by Karen Stewart, other reasons include (1) it prevents soil erosion by reducing rainfall runoff, (2) it conserves energy that would be used for potable water processing, and(3) it fosters a greater appreciation of nature.

How to harvest rainwater, broken into four main categories.

1.       Collection,

2.       Conveyance,

3.       Storage,

4.       Distribution.


Collection is accomplished by placing gutters on all roof surfaces: house, stand-alone garage or carport, shops, storage buildings – any roof area on which rain falls.  Hardware cloth, with about ¼” mesh size helps keep leaves, bugs, etc. out of your system. 


 Conveyance is via downspouts and underground piping, which send the water to a roof washer and, thus to your storage tanks or sump tank.  Whether you need sump tank depends on whether there is enough head for gravity to get the water into the storage tanks rapidly enough.  If not, gravity sends it to a sump tank and a pump with a float valve sends the water from the sump tank to the storage tank. A roof washer is a device that wastes or cleans the first flush of rainwater off the roof, since the first flush will contain most of the dirt and debris that makes it through the hardware cloth.  However, some systems in WCE use special filters in the openings of the downspouts and avoid formal roof washers.  Our system does not so I can’t speak to them.  The two other types of first-flush treatment, with which I am familiar, are pre-tank filters and first-flush diverters.  Our system was bought from Tank Town.  At that time, they only had the pre-tank filter system, which comprises a fiberglass box containing two filters that remove anything larger than 30-microns (µ, one µ is about 0.00004 inches or one-hundredth the thickness of a human hair), before the water ever enters our tanks.  These filters, when clean, will handle a lot of water so that none is wasted during a hard rain.  After the rain event, the filters can be removed, power-washed clean, and reinstalled.  First-flush diverters, as the name implies, divert the first several tens of gallons to a separate little tank so that the first flush doesn’t get into the storage tank.  The water in the diverter tank can later be drained and used for watering plants.


There are several types of storage tanks, ranging in price from relatively inexpensive poly tanks, more expensive fiberglass tanks (which we have because it was recommended when we bought our system), to even more expensive metal tanks with a bladder.  All will work and have a relatively long life expectancy.  Tank Town, if you’re driving out Hwy 290 toward Henley, has a number of fiberglass tanks, some painted quite nicely, for their rainwater bottling facility.  The Dripping Springs Library also has a very attractive fiberglass tank – it has a turtle painted on it.  If poly tanks are used, be sure to get black, instead of white or translucent, to avoid algal growth inside the tank.


From the storage tanks, our water is pumped, on demand, to the house for our use.  On the house side of the pump, the water goes through a 5-µ filter, a 3-µ activated charcoal filter (think Britta), a 1-µ filter, and, finally, an ultra-violet light, before it actually enters our house.  The 5-µ keeps the charcoal filter from getting clogged and should be changed monthly.  The 3-µ, since it contains activated charcoal, removes any odor or taste that might be associated the filtered water - changed quarterly.  The 1-µ is less commonly used in a system but basically removes any constituent that is not dissolved in the water – changed quarterly.  The preceding is for drinking water.  For watering your garden or flowers, you can pump or drain right from the storage tank(s).   The UV light is changed every 12 to 18 months and kills everything that might be in the water, without adding any chemicals.  There are other treatment methods – chlorination, ozonation – but we found UV to be the simplest and it is very efficient.

Getting Started and General Information

The simplest rainwater harvesting system is a rain barrel under a downspout (be sure all barrel openings, except the discharge, are completely covered with window-type screening so you don’t create a magnificent mosquito breeder).  At the other end of the spectrum, a number of schools now collect rainwater; Home Depot on RR 620 has several huge tanks; Zilker Gardens supplements with rainwater collection, as does the Lady Bird Johnson Wildlife Center.  If you drive around and look closely, you will see that a number of our neighbors have rainwater collection systems.

How much storage do you need? 


This depends greatly on how you think about water.  If the water runs while teeth are being brushed, if water-saving appliances are not used, and a lush St. Augustine lawn is desired, you probably only want to consider rainwater harvesting as a supplement or move to deep East Texas or build a large rain barn, as at Tank Town.  If you’re conscientious about water usage: water-efficient appliances, xeriscape as much as possible, , use low-flow showerheads and low-volume toilets, and shower long enough to get clean but not long enough to sing your way through several arias, you can easily get by on 40 gallons of water per person per day.  My wife and I plan on 2,500 gallons per month or about 2,500 x 12 = 30,000 gallons per year for the household and that includes some visits by kids and grandkids and maintaining what we consider an attractive back and side yards with flowers to attract hummingbirds and butterflies.  According to the Karen Stewart article noted above, it takes about 30,000 gallons to provide a one-inch watering to the typical home lawn and, according to an internet site on St. Augustine grass, one should water between ¾” to 1” every other day in the summer for a healthy St. Augustine yard.

But what if it doesn’t rain? 

Well, there are a number of local suppliers that will deliver 1,500 to 2,000 gallons of good water (not as good as rainwater but acceptable, even for those spoiled by rainwater) for $65 to $90 (the last time I bought water).  If the drought is severe and we work at it, we can get by on around 2,000 to 2,100 gallons a month, so it’s not that expensive if you must buy.  When there’s no drought, your cost is the price of the filters and the occasional UV lamp, plus what little electricity it takes to run the pump.

How much water can one collect? 

There are formulae on the internet to calculate that or you can remember back to high school physics and figure it out (sure we can!).  I used the information from “Rainwater Collection for the Mechanically Challenged” by Suzy Banks with Richard Heinichen, which is available at Tank Town and is very helpful if you’re considering rainwater harvesting – answers questions you didn’t know to ask and is amusing to read.  As noted in the above-cited booklet, an inch of rain yields a maximum of 562 gallons of water per 1,000 square feet covered by your roof area.  That last phrase may seem clumsy and convoluted but it’s not the area you have to pay your roofer to cover but the area of ground covered by your roof that determines how much rainwater falls on your house.  For example, two inches of rain falling on a roof that covers 3,000 square feet of ground will yield a maximum of  2 x 3 x 562 = 3,372 gallons.  But you won’t collect the maximum because gutters are not 100% efficient, there is evaporation, the stand pipes and underground system hold water which does not get into storage, etc., so assume about a 25% loss for calculation purposes.  Our system is more than 75% efficient, when I keep the gutters free of oak leaves but our standpipes and underground piping hold about 170 gallons.  Once they are full, we collect about 1,600 gallons per inch of rain.  Since we need around 30,000 gallons per year, we need to live in a location that gets at least 30,000/1,600 or approximately 19 inches per year.  Austin, with an average annual rainfall of around 32” should work fine and it has for all but one of the last 12 years we’ve been in WCE using rainwater collection.  Theoretically, with a large enough collecting surface and sufficient storage, rainwater harvesting would work anywhere on earth.

Much of the preceding, that was not based on personal experience, was stolen (sometimes blatantly) from “Rainwater Collection for the Mechanically Challenged”, the Tank Town website (www.rainwatercollection.com) ,  and the Rainwater Harvesting Community website (www.harvesth2o.com).  Wikipedia has some fun information on rainwater harvesting in the past; e.g., 300 BC, and around the world (every continent except Antarctica).

If you would like to see a system in action, send me an email via this WCE HOA website (treasurer@westcaveestates.com) and we can work out a time.


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