It’s great to see all these urban farms blossoming across the open lots and schools in the Bay Area. They are producing healthy and tasty lettuce, tomatoes and assorted vegetables for high-end restaurants and local farmer markets. Being close to markets they have a small carbon footprint in transportation costs. And, they are credited for bringing fresh food to areas that have been classified as urban food deserts. Despite all these positive attributes, have you ever considered how much water is needed to grow these crops, where the water comes from and what the cost of that water may be?
How much does urban water cost? Looking at rates from East Bay Municipal Utility District, non-potable water, the least expensive and least processed form of water, costs $3.78 per 100 cubic feet. For the sake of argument, let’s consider a one-acre, urban garden plot; its dimensions would be 208 feet by 208 feet and it would occupy 43,560 square feet; this area is slightly more than half the size of a soccer field or the contingent area of seven tennis courts. This would translate into one-acre foot of water costing $1,646. If you are using potable water, the cost is $4.85 per 100 cubic feet, or $2,112 per acre-foot. I would think the average person on the street would be surprised to hear these costs.
In California, vegetables need irrigation water to grow as it does not rain during the growing season, April through September. In practice, many vegetables need an application of water 2 to 3 feet deep to complete their life cycle, so on a volume basis this would add up to 2 to 3 acre-feet of water.
So, how does the water cost translate to the yield and price of vegetables you may grow in your urban garden, like lettuce for your salad? Lettuce needs about 3 feet of water with conventional irrigation (sprinkler, flood or furrow). Consequently, the cost of 3 acre-feet of water for lettuce growing in a city is nearly $5,000. Of course, the cost of water will scale with the size of the urban garden plot and be less with smaller gardens. In comparison, the wholesale market value of an acre of lettuce produced by a farmer in the Salinas Valley is between $6,000 to $8,000. While the net margin difference in receipts and cost of water is still positive, it does not consider added costs of labor, value of land, seed and machinery to till ground.
How do these abstract and rather large costs translate to you and me and the price of head of lettuce we want to buy for our fresh, tasty salad? In general, lettuce fields, such as those in the Salinas Valley, produce about 26,000 heads per acre. If you are an urban farmer with similar yields, your water usage will add up to a cost of about $0.18/head. In comparison, with gross receipts at the farm scale for a crop of lettuce is about $7,000. This translate into the farmer receiving about $0.26/head. Such gross receipts would leave almost no profit margin for an urban gardener who is selling one’s goods on the wholesale market. In comparison, the price of lettuce in the market is much greater. You may you pay $1.50 to $2.00 per head at the grocery store. When you eat a lettuce salad at Chez Panisse, you may pay $9 a plate.
While $5,000 for the water to produce an acre of lettuce in an urban environment may sound exorbitant, when we look at its value on a price per piece ($0.18) compared with the price you pay in the market ($1.50-$2.00) it may be cost effective to produce fresh food in urban gardens if one can sell their product for a premium price in the local markets. But, then this may not make the food as affordable as needed by those with limited incomes.
Large-scale farmers do not pay these high prices for their water. Those operating in the Central Valley have access to highly subsidized state and federal water sources, which translates to cheaper food costs in the store for you and me. I performed a survey of published irrigation water rates for districts across the Central Valley for the period between 2010 and 2015 and found that the average cost of water was about $40 acre-foot. Some irrigation districts have access to much cheaper water. The Central California Irrigation District, with access to Bureau of Reclamation Water, charged farmers $15 per acre foot for the first 3 acre-feet of water they used (http://www.ccidwater.org/2017%20Water%20Supply%20Jan%2024.pdf).
Because water is so inexpensive at the farm scale, there may be inefficiencies in irrigation and harvesting at the farm scale that do not translate to the small urban garden. Consequently, there are ways an urban gardener can reduce the amount of water applied and purchased. One may only need 1.5 acre-feet to produce a crop of lettuce with drip irrigation, which bring us to a cost of $2,469 for irrigation water. Irrigation efficiency can be improved by reducing soil evaporation with mulches, irrigating at night, scheduling water applications to match previous water use, and increasing soil water holding capacity with compost. One may also capture and store rain runoff from roofs during the winter. But one will need to consider the added cost of storage, including the container and expensive land.
The take-home points are listed in the following: 1) is it is important to know all the costs when implementing urban gardens, as there is no free lunch, or free water; 2) we should seriously consider more efficient irrigation methods, as the high cost of water makes their capital expense more worthwhile, and 3) we should have access to cheaper less processed water for our urban gardens. Finally, urban gardens produce many social and educational goods that may transcend the cost of water. These include local land stewardship, awareness of healthier diets and access to fresh and better food.