There is a bill in the Colorado House of Representatives – again – to allow Coloradans to collect rooftop runoff into rain barrels to use on their lawns and gardens. Colorado prohibits retaining rainwater, and it’s one of those quaint things that is uniquely Coloradan because of Colorado’s fate as the place where seven river basins provide water for a half-dozen states.
There is a reason for the rainwater prohibition. Old hands in the water business say capturing rooftop runoff keeps water from returning to the rivers and other aquifers. I didn’t say it was a good reason, but that’s the one that is cited. Guardianship of existing water law and water use tradition is never-ending, like any form of husbandry, and so the water shepherds will oppose the bill and impose restrictions on it and well they should. The doctrine of prior appropriation isn’t just a legal concept, it’s a statement of faith in an environmental principle that’s been around since Thoreau waxed poetic about Walden Pond. It’s foundational, it’s almost scriptural (“First in time, first in right” saith the Lord.) and it needs to be defended as sacrosanct.
But that defense should still be rooted in science and practical application. No one, to my knowledge, has ever presented scientific evidence that retaining rooftop runoff would materially harm the rivers of Colorado. I have it on good authority that Colorado State University has run a computer model that shows capturing rooftop runoff would have no discernible effect downstream. My sources tell me, however, that minimal effort was made on the study, it used EPA storm runoff data (using federal data on local water issues is almost always an apples-and-oranges proposition) and that the arithmetic in the thing is questionable. By the same token, however, I’ve never heard a scientifically sound reason for dipping water out of a rain barrel when you can hook a hose to your house with a fraction of the effort.
I’m not a hydrologist, but I’ve hung around the various philosophers, saints, and sinners who govern water use in Colorado long enough to soak up just enough knowledge to be dangerous. I know that watering lawns and gardens in town is called “consumptive use,” which means none of the water returns to the river or aquifer from whence it came – it all gets used by the plants or evaporates directly into the atmosphere.
I also know that this is not a simple matter of water flowing or not flowing into a nearby river. There are vast stretches of eastern Colorado where there are no rivers and that use water pumped from closed aquifer systems; no amount of water running off of rooftops is going to replace what gets pumped out for irrigation and municipal use. In other parts of Colorado water is pumped from aquifers that support rivers, like the South Platte and San Luis valleys. Still others, like most mountain communities, use water directly from river and tributary runoff.
A combination of sources is used to supply the northern I-25 corridor, an area about 100 miles long and 50 miles wide that contains between 70% and 80% of the state’s population, depending on who’s doing the counting. This area pumps from the Denver Basin Aquifer, a closed system that can’t be recharged by runoff, and from the South Platte Aquifer, which supports the South Platte River. It diverts water from the Colorado River via the Colorado-Big Thompson Project, and pipes it from high mountain reservoirs.
With such a diversity of water sources, it’s difficult to say whether capturing rooftop runoff would have a discernible impact on streamflow. Out on the eastern edges of the state, where water comes mostly from the Ogallala Aquifer, capturing and storing rainfall runoff might actually help slow the depletion of the aquifer. Scientists estimate that, even if all of the rain and snow that fell was allowed to soak into the ground, it would take 6,000 years to recharge the aquifer. Given the arid climate and the fact that much of the aquifer is covered with impermeable caliche clay, and since the aquifer actually was formed and filled millions of years ago, it may be impossible to recharge it at all. Using rooftop runoff could actually increase the water supply in those areas – if enough fell to make a difference.
In areas where water is pumped from river-based aquifers or is piped straight out of the river, it makes sense that rainfall and snowmelt would be needed to replenish the water sources, but even then some simple arithmetic could tell a different story. Take, for instance, my hometown of Sterling, on the South Platte River up in the northeast corner of the state. The city of Sterling pumps water out of the South Platte River Aquifer, which is the same as pumping it out of the river – as the aquifer is drawn down, the river level drops, a phenomenon that can be viewed by standing on any bridge across the river in August. And so it would seem that a little arithmetic could at least provide a starting point to argue for or against the capture of rooftop runoff.
First, let’s assume that all watering of lawns and gardens is 100 percent consumptive use. Let’s pretend that at least 110 gallons of rain falls on the roof of your house every week and what doesn’t leak in through the skylights and cause mold in the attic gets captured for consumptive use on the lawn and garden. That water is then used to irrigate your yard, and none of it gets into the river. However, I’m also going to assume that for every 110 gallons of water used from rain barrels, an equivalent 110 gallons of water stayed un-pumped from the city’s wells every week and that same 110 gallons of water not pumped from the river’s aquifer would then flow downriver and, in fact, replace the 110 gallons collected from the rooftop. Multiply that by 1,000 households, and you have 110,000 gallons of rainfall that isn’t going back into the river, and 110,000 gallons of water not being pumped out of the river.
The truth is, that’s just swapping one kind of water for another; you can call it conservation if you want to, but what it really looks like is something called “augmentation.” That’s when water that’s used consumptively is replaced with water from another source. It was pioneered in irrigated farmland to try to minimize or even offset impact on the river from pump-fed irrigation. A typical augmentation plan has water taken out of a river during fall and winter, when no one needs it to irrigate with, diverted to ponds or watercourses miles away, and allowed to seep back into the ground. In theory, the water seeping into the ground will flow back toward the river and reach it at about the time it’s needed to irrigate crops in the spring and summer. Another way augmentation works is to find water somewhere other than in the river, such as captured rainfall , and use that instead of pumping water out in the first place.
But augmentation isn’t really conservation. Water conservation means using less water, not swapping out water sources. So using rooftop runoff isn’t water conservation at all, it’s just using water you would have used anyway, only without running it into the aquifer and pumping it back out. People who truly want to conserve water, especially on outdoor plantings like lawn, garden, and trees, don’t use sprinklers at all; they use drip systems and soaking hoses. At my house, all of our trees are on drip systems that deliver water directly to each tree’s dripline. The vegetable garden is watered with soaker hoses on a timer so water is delivered directly to the ground and at a time when it won’t evaporate into the air. We don’t even have Kentucky bluegrass in our lawn; we have only native prairie short grasses, which require little or no watering.
Still, there’s just something about collecting rain in a barrel that feels good, that feels like it should be a good thing or, at the very least, a natural right to capture God’s gift from the sky and use it to green up one’s very own little ecosystem. And for that reason, the water barrel bill probably will pass this time. My personal prediction is that we will see a sudden plethora of 55-gallon drums decorating suburban homes next summer, followed by widespread complaints of mosquito infestations, and finally a new trend of marigolds planted in 55-gallon drums.
So yes, let there be water collection barrels, by all means. But don’t expect it to be the wave of the future. It will be a sap to a few granola-crunchers who don’t understand hydrology, and it will be one less reason for Colorado to appear on those lists of silly state laws. And as far as I’m concerned, that can’t happen soon enough.