The economics of my rain tank

Last winter was my first with a 530-gallon rain tank. I did not buy it because I thought it would save me a bunch of money on my water bill. I bought it because rain coming off my roof and running down the driveway irritated me. It seemed wasteful. Water is scarce and expensive in Southern California. But now I find myself wondering whether the rain tank will eventually pay for itself.

Bushman Slimline 530 gallon

The tank is a Bushman Slimline, and it cost $615. The accessories needed to connect it to the gutter and direct overflow (pipes, joints, straps), plus a ball valve to distribute the collected rain into drip lines that irrigate my vegetable garden and some fruit trees, as well as the gravel for the tank’s foundation all cost about $30. So, excluding my time and excluding sales tax, the tank system cost $660.

The tank collects from a 363 square-foot section of roof covered in concrete tiles, which have an efficiency estimated at 65%, meaning 35% of the rain that falls on the roof is not shed into the tank. In other words, though 226 gallons fall on this area of roof per inch of rain, only 147 gallons are shed into the tank.

In an average year of rainfall we get 16.43 inches. So in an average year we’ll collect 2,415 gallons in the tank. If I bought 2,415 gallons of water through our municipal water district it would cost $17.81. At that rate, it will take 37 years for the tank to pay for itself. That’s depressing.

However, I’ve started to think of comparing rainwater to municipal district water as comparing apples to oranges. They’re different products. The quality of the municipal district water is far lower than the quality of the collected rain in terms of the characteristics that plants care about: chloride levels, total dissolved solids, pH, electrical conductivity, etc. And so, the value of a gallon of rainwater is higher than a gallon of municipal district water — to plants, at least (and that’s who’s getting my rain tank water).

To this point, a study of banana plants in Israel found that the highest yield that could be obtained when using “freshwater commonly used for irrigation” (similar to our municipal district water) could be obtained with about half the amount of desalinated water. In other words, if 5 units of desalinated water are needed to grow a banana, then 10 units of irrigation water would be needed to grow that same banana. The desalinated water is twice as valuable to the banana plant.

Similar to desalinated water, rain has very low levels of salts, and rain is more valuable to plants than our municipal district water. I think we already know this from experience. We give the plants in our yard a couple inches of water from a sprinkler and the plants look good, but after a real storm rolls through and drops a couple inches of steady rain our plants look amazing — they’re standing so tall and firm and shiny — and they don’t seem to need more water for weeks. There’s something magic about rain.

So, what if I value the rain that I collect in my tank at twice the price of district water? At that rate we’re looking at just under 19 years until it pays for itself. That’s still a very long time.

The price of the water from the district keeps going up though. I just got a letter informing me that the rate will increase again on September 1. This rate that becomes effective on September 1 will be a 20% increase from the rate we paid when we moved in only two years ago. That’s a 10% rise per year, so far.

If I use the rate that will be effective in September (and continue to value rain at twice as much as district water), the tank and its system will pay off in about 15 years.

Furthermore, as far as I know, the price of water in my district has never gone down. I’m guessing that it will only continue to rise. If it continues on its trajectory of 10% per year, then we’re looking at a pay-off length of ten years.

Ten years is still a long way off, but it does sound reachable. And even though I didn’t buy my rain tank as an investment (thinking it would save me a bunch of money on my water bill), I do now feel less indulgent about my purchase.


Related posts:

Sizing rain tank #2

A new year, a new rain tank, a new weather pattern

Rain is not sewage

Reusing laundry water

Puleng laundry

This is Puleng, one of my former students in Lesotho. I learned to wash by hand from her and other students at Ngoana Jesu Secondary School, and I also learned from them to reuse my laundry water on my vegetable plots. I adopted that practice in Lesotho, and I’ve been trying to adapt it to my new context in Southern California.

Here I use a machine to do the washing, and I reuse the laundry water by directing it through a hose to a Chinese pistache tree.

laundry machine

But in getting from the Lesotho method to this California method, I made a few mistakes along the way.

When we moved into our house  — almost two years ago, now — I disconnected the hose behind the washer so that instead of emptying into the sewer line I could empty it into a trash can. I then used a bucket to distribute that water to our burgeoning vegetable garden. It took a lot of time to distribute that water, however. The washing machine used more than three times as much (each load used between 15 and 30 gallons whereas in Lesotho each load used between 4 and 7 gallons).

So last spring I bought an extension for the machine’s plastic hose. I planted tomatoes, squashes, and melons in four groups along the driveway, fairly close to the washing machine, and I placed the end of the hose near one of the groups of plants each time we did a load. The plan was to water all of those plants with laundry water alone. Then the plants started dying. The young squash plants started showing symptoms first. The margins of their leaves looked burnt, and the plants grew very slowly in general. Next the tomatoes demonstrated toxicity. They screamed toxicity! Their leaves yellowed, purpled, curled, they stopped setting fruit, and so I yanked them out of the ground.

We had already switched to using the least toxic detergent we could find (Ecos brand), so then we cut back on the amount of that detergent we were using. It was all too late. The soil had been spoiled and the plants were goners.

I thought about why these vegetables were killed by my laundry water while my vegetables in Lesotho had thrived under an apparently similar regimen. Turns out they weren’t similar regimens.

In Lesotho, I often dumped the wash water in the bushes and only the rinse water on my vegetable plots. Yet here in California I was dumping both, so it added potentially harmful chemicals in higher concentrations. But more than that, I hadn’t used as much detergent in Lesotho in the first place. When washing by hand, you see how soiled each article of clothing is and you only apply as much detergent as is absolutely necessary. Having to work with your hands in such a detergent solution encourages you to use as little as possible because the skin on your fingers and palms get tight and painful if you use a lot. Now using the machine, we were just unthinkingly following the recommendation of the detergent manufacturer (“fill to this line”) and thereby adding much more detergent than we had while washing by hand in Lesotho — this even though the Ecos brand ingredients were much less toxic than the ingredients of the Surf brand that we used in Lesotho.

Another difference that occurred to me was that in Lesotho it rained all summer. There were thunderstorms which consistently leached the laundry water through the soil profile. In addition to that, when the rains failed, I watered my vegetables with collected rain off my roof and the school buildings’ roofs, as well as groundwater from a borehole pump. Yet here I was in California giving my vegetables a steady diet of nothing but laundry water.

Therefore, we come to our current method of reusing laundry water in the yard in Southern California.

For almost a year now, I have experienced excellent results by connecting a short extension hose (15 feet long) to the washing machine and snaking it under the Chinese pistache tree behind the garage. This tree receives additional rainwater all winter from the runoff from the nearby concrete porch as well as two roof downspouts, and thus the soil gets a leaching similar to what my Lesotho soil received. We place the hose near the spots where the porch and downspouts concentrate their rain runoff.

laundry hose placement

Whatever chemicals build up over the summer from laundry water (sodium is the particular chemical in Ecos detergent that I’m worried about) will be leached by the rinsing of clean rainwater through the winter. That’s the theory, anyway. So far it seems to be working out based on the fine appearance and new growth of the tree.


After we’ve finished with each laundry load, we hang the hose extension on the wall so it drains completely. This ensures that there is never any bad smell — for even a little laundry water sitting in a pipe will start to stink.

laundry hose

Why haven’t I installed permanent piping to direct the laundry water to the pistache tree? Seems like that would save the time of having to connect the flexible hose before each load and then having to hang it back up afterward. True, it would save that time, but that time adds up to literally five seconds. The task is so quick and not annoying that we don’t even think about it anymore.

But more importantly, there is only a single inch of fall between the level of the concrete porch and the soil surface beneath the pistache tree. Therefore, pipes would have to open into holes dug deep enough such that the pipes are sloped enough to drain completely. These holes would need to be maintained so they don’t clog the pipe outlets.

The permanent system would save the few seconds we spend connecting and disconnecting the flexible hose at the expense of the time and resources it would take to install (cut concrete, buy and lay pipe, dig outlet holes, etc.) plus maintain. As for now, the flexible hose method requires zero maintenance, has no chance of becoming clogged, and yet remains adaptable to additional plantings we might make in that part of the yard in the future.

Saving water by applying urine as fertilizer

I balked at the idea of urinating into a toilet bowl of fresh, drinkable water when I first returned from Lesotho. Not that I’d forgotten that was the norm in America. I’d done it my whole life until moving to Lesotho. But as the G.K. Chesterton quote goes, “The whole object of travel is not to set foot on foreign land; it is at last to set foot on one’s own country as a foreign land.” For the first time I saw it not just as going to the bathroom, but as urinating into a toilet bowl of fresh, drinkable water. To this day, it seems ridiculous. I generally avoid it. I’m wondering though — How much water do I save by feeding the plants instead?

On average, a person urinates five times a day, and the toilets in my house use the standard 1.5 gallons per flush. This adds up to eight gallons a day, or about 250 gallons a month, or 2,920 gallons over the course of a year. That sounds like a lot.

But I haven’t saved that much. I can make a wild guess and say I haven’t used a toilet half of the time (I’m often at work or at someone else’s house), and I’ve been back from Lesotho for seven years now. Over those seven years that would add up to about 10,000 gallons.

Just for fun I can calculate the cost of that. At my current rate of $0.007673797 per gallon, that comes to $76 worth of water.

But I really don’t care about the cost. The cost is secondary to the insanity of using a bowl of water that has been transported thousands of miles from the Rockies or the Sierras and filtered and treated and pumped through millions of dollars worth of infrastructure to get to my house only to be pissed in and flushed into the septic tank. The stupidity of that kills me.

It especially kills me because there is this simple alternative of walking outside and feeding the plants. Or there’s the option of letting the yellow mellow, which is at least a little less stupid.

There’s talk all over the place of changing our habits because of the drought. There are signs on the roads: Severe drought. Save water. And our water district mandates that we only water three times per week between the hours of 6 p.m. and 10 a.m. The University of California, San Diego is converting some median strips of turfgrass over to lower water plants, and they are advertising it everywhere, congratulating themselves for their immense awareness. The governor made his big show of demanding 25% cuts in use. (I’d like to see how he uses water on a daily basis.) He calls this a “State of Emergency.” Water is scarce; we must conserve what little of it we do have. Meanwhile, we piss in it five times a day?


Related Posts:

Urine as fertilizer

Applying urine as fertilizer

The water economics of homegrown avocados

The water economics of homegrown avocados

I heard a Master Gardener say she was hesitant to recommend that people plant avocado trees in their backyard because of their high water needs, as we’re in a drought. Sounds sensible. But unless you’re also going to stop eating avocados, then you haven’t automatically saved water just by not growing avocados in your own yard. You have merely paid an avocado farmer to use the required water to grow avocados in his grove.

Moreover, if you’re buying “local” then this avocado farmer might literally live within walking distance of your own yard and be using water from the exact same sources as you would.

So what if you did plant an avocado tree in your yard instead of paying a farmer to grow your fruit. How much water does an avocado tree need? And how many avocados would you get for that water?

According to Gary Bender, former farm advisor with the University of California Cooperative Extension, a mature avocado tree with a canopy of 20 feet in diameter requires about 10,000 gallons per year. This is for the environmental conditions of Escondido in San Diego County. We receive some of this required water in rainfall each year, but for the sake of argument let’s say we have the driest year in history and don’t get a single sprinkle; we have to use irrigation water for the entire 10,000 gallons. How much would that cost? At my rates it would cost $75.53.

How many avocados can I expect from a tree that I give $75.53 worth of water? Again according to Bender, a mature tree of the Hass variety will produce about 200 fruit each year on average. That means each avocado would cost $0.38 in water.

Avocados from the grocery stores near me go on sale for as low as $0.50 for small ones, but are usually $1 each. Large avocados are always at least $2 each, and normally around $3. These are not for avocados labelled “organic,” which are of course more expensive. The 200 fruit you get on a tree in your backyard will vary in size from small to large, so let’s estimate an average retail value of $1.50 per fruit, meaning the 200 fruit on your tree would have a retail value of $300.

You put in about $75 in water to get $300 worth of fruit so you’re left with $225 per year to account for costs other than water. The initial purchase price of the tree, irrigation equipment, time spent harvesting, and the bags of fruit you’ll give to friends won’t come close to $225 each year.

Seems clear to me that if you eat avocados, and your climate allows, you should be watering a tree in your own yard.



You might also like to read:

How long until an avocado tree fruits?

Do you need two avocado trees to get fruit?

Can you grow an avocado tree in a small yard space?

The Economics of Homegrown Broccoli

I’ve long assumed that it is more expensive to grow vegetables at home compared to buying from the grocery store. I do it for other reasons, I tell myself. I feel rich having food growing around the house, I like getting my hands in the dirt, it’s fun to send friends home with some produce after they visit, and I know what’s in and on the food I eat from the yard.

However, I realized that I’ve never actually done the math. Thomas Sowell spurred the thought — I’m reading his great book, “Basic Economics.” Where are the hard facts? as he asks.

At a couple of grocery stores I noted prices on broccoli, which is what we happen to have a lot of in the yard at the moment. At Albertson’s, it was $2 per pound. I weighed a small head and a large head, and they were 0.75 and 1.75 pounds respectively. Therefore, a small head would cost $1.50 and a large head $3.50. Then I checked prices at Whole Foods. They didn’t have heads of broccoli, but they were selling bunches of about ten side shoots each for $3. The bunches were about the same size as a medium head, so let’s think of it as $3 for a medium head at Whole Foods.

That’s the cost of broccoli at the store; now what does it cost me to produce broccoli at home? This year, I started some from seed and some as transplants bought at a nursery, but for simplicity’s sake let’s only use the cost of the transplants, which were $3 for a six-pack, or $0.50 per plant.

The plants needed water. But since they were grown during our rainy season the water inputs were small. I planted on September 19, and then I irrigated a total of 18 times before the rains became consistent enough to make irrigation unnecessary, and I began harvesting in December. The total irrigation per plant before December was about eight gallons, costing me $0.06.

How about labor? In addition to planting the seedlings, I added compost to the soil surface, and I programmed the automatic irrigation system. I actually never had to weed because the beds I grew the broccoli in have been well cared for in the past. And then I harvested. Per plant, the total work might have taken four minutes. (Important note here: I encountered zero pest damage this year even though last year I lost some broccoli plants to rabbits and later in the season some plants suffered aphid damage. But let’s just talk about this year’s facts.) What was my four minutes of labor worth? I could’ve been teaching, where I make about $30 per hour, in which case four minutes to me is worth $2.

Adding up all the costs, we have $0.50 for a seedling, $0.06 for water, $2 for labor, and I’d like to estimate $0.20 for irrigation infrastructure and compost. Total cost: $2.76 per broccoli plant.

Again, I found that a small head at the store cost $1.50 and a large head cost $3.50, but broccoli plants grown in the yard produce much more than just a single head of any size. Mine were the variety ‘Premium Crop’, and they produced two to three medium-sized heads plus side shoots for months thereafter. (It’s mid-February and I’m still harvesting side shoots galore.)

Broccoli side shoots galore

‘Premium Crop’ side shoots galore

I’d estimate I got a retail value of $7 to $10 out of each plant.

By these calculations I’m ahead a minimum of $4.24 per plant. And that really surprises me. While it surely varies year to year and plant to plant, this year homegrown broccoli is not just cleaner and fresher than broccoli from the store, but more economical as well.