Rainwater Harvesting for Drylands and Beyond by Brad Lancaster


This section of the website and its content are still very rough. This is the beginning of a process to create water-harvesting curriculum, and these first exercises are just rough drafts. More are still to come. But in the meantime, give them a whirl and send us your feedback (to brad@harvestingrainwater.com) so we can improve them. They are all meant as exercises to go with readings from Rainwater Harvesting for Drylands and Beyond, Volume 1.

And for additional passive water harvesting activities visit Catch the Rain!

The following curriculum has been developed by Kent and Diane Sorensen, Brad Lancaster, and others.



Students consider the different sources of water entering a landscape.  They then calculate the amount of water resources available at each point to arrive at the total yearly amount of water for use in the landscape. In the process, students discover that each site is a watershed and that we can manage the flow of that water.

To demonstrate for students how each site is a watershed unto itself, and to facilitate the students’ discovery of the sources of the water resources within that watershed.

•    Students will discover the sources of rainwater (rainfall, stormwater run-on and run-off) entering and leaving the site.
•    Students will discover the sources of graywater (all household drains except dishwasher and toilet, which are blackwater, or discharge from water softeners which is too salty) for use in the landscape.
•    Students will calculate the amount of on-site, non-potable water available for the landscape – rainwater [rainfall run-off/on], graywater [bathroom sink, washing machine], clearwater [reverse osmosis, air conditioner condensation], salty water – lowest quality [evaporative cooler bleedoff].
•    Students will point out areas with more water as well as dryer areas in the landscape.

•    About two hours for all four exercises, but they could be broken up and done separately, though in order.

•    A mound of approximately 2 wheelbarrows’ worth of soil
•    Calculators
•    Notebooks

• “Rainwater Harvesting for Drylands and Beyond, Volume 1” – chapters 1 and 2.

– WHAT IS A WATERSHED? AND HOW TO IDENTIFY ONE with the dirt pile model

Construct a mini mountain-side watershed (and its sub-watersheds) on a small earthen mound. (More or less mimic the illustration in Figures 2.1A,B,and C in Chapter 2). A short video of this exercise will also be posted on the video and/or curriculum page of www.HarvestingRainwater.com
Make three distinct watersheds on the model with your topography – the first two watersheds being subwatersheds of the third, and largest watershed that will encompass all three.
Place a stick at the base of each watershed (you will ask students to identify the ridgeline of each watershed (surface flow only) for each stick. Make the topography distinct.

•    Gather students around model.
•    Ask: What is a watershed? (Answer: The total surface area draining to a certain point.)   Solicit answers from students.
•    Describe and point out local watersheds seen from the site (look to mountain ridgelines on the macro-scale and roof ridgelines on the micro-scale).  Point out which slopes drain toward students, and are part of the watershed they are standing in; and which slopes drain away from students, and are part of another watershed.
•    Explain that the ridgeline is the boundary of the watershed.
•    Now focus on the dirt model. Ask individual students to trace with their fingers the ridgelines or the boundary of the first (and highest) watershed for the first stick on the earth mound. See if they get it. Can they correct each other if needed?
•    Once the first watershed is understood, proceed to the second stick and have a different student trace its ridgeline.
•    Once the second watershed is understood, proceed to the second stick and have a different student trace its ridgeline. This last point, and its watershed, should encompass almost the entire watershed of the model. Point out that each of the previous points/watersheds were sub-watersheds of this last/largest watershed.
•    Any questions. Stress the importance of breaking up watersheds into sub-watersheds to more easily slow, spread, and sink the flow of water (reference 8 Principles of Successful Water-Harvesting from Chapter 1).
•    Solicit feedback from the rest of the group.
•    What are the watersheds and sub-watersheds of this site?
•    Now direct students’ attention to the site, and ask, “Where is the top of the watershed directing water to where we are standing?” (Roof of house?, property line, or above property line? – if so start at the top of your watershed of influence – the property line and start talking with neighbor).
•    Ask, “Why is it important to start at the top?” (Work with gravity, harvest water throughout the site, rather than just the bottom)
•    Transition to the next exercise by explaining, “We are going to determine the sources of the water that feed this watershed. Once we determine where the water comes from in our watershed, we can make choices about how to use it as a resource.”




1.  If possible, take students up to the roof of the watershed – often the roof of a house or classroom. Be careful in climbing up, be sure no one is hurt. (The intent is to start literally at the top of the watershed.)

•    What are the sources of water that drain – or could potentially drain — onto the site/landscape below?
(Students ought to mention rain. But try to get them to see evaporative cooler bleed-off, and/or air conditioner bleed-off, run-on from other properties, other roofs, or hardscapes such as patios, sidewalks, and driveways.)
Ask, “Is this water currently being utilized or wasted?”
Re-emphasize the 8 Principals of Successful Water Harvesting (refer to Chapter 1 of Rainwater Harvesting for Drylands and Beyond, Volume 1).

2. Get back on the ground and have students walk the watershed and sub-watershed boundaries. Have them track where the water (all potential on-site water sources) goes, its direction, where it comes from. What areas of the landscape does it water? What areas does it drain or erode? See if students can identify which parts of the landscape are supplied with water from which watersheds. Also track potential or existing greywater sources.

•    Look around the area directly off the site – perhaps just off property. Do you see where water might flow onto the site? Off the site? From roads, sidewalks, other roofs, other yards, higher ground? Note gutters, downspouts, erosion and water tracks or detritus build up).

•    Aside from rainwater, are there any other sources of water for this site?  (Try to lead students to discovering any possible graywater sources). Refer to estimated greywater flows in Box 2.6 in Chapter 2. What is easily accessible? (Washing machine, drains against exterior walls.) Impractical? (Interior drains encased in concrete slab.) Mention that making an outdoor shower is an easy way to access graywater.



•    Divide students into groups. Have each group pace off a different area/catchment/sub-watershed to find square feet or square meters of each catchment area (roof/sections of roof, driveways, patios, run-on areas, entire property). You could also give student to-scale plans of their catchments after they pace off their catchments.

•    Have the students calculate how much rain falls on their catchment in a typical year of rain. Refer them to Box 2.3 and/or equations 1 through 4 in Appendix 3 of Rainwater Harvesting for Drylands and Beyond, Volume 1, to calculate the yearly rainfall on that specific area. If some groups are fast, have them calculate how much rain will fall on their catchment in a given rain event – typical large storm for the area.

•    Have another group calculate the potential greywater flow into the landscape using Box 2.6 and Box 2.7 from Rainwater Harvesting for Drylands and Beyond, Volume 1. Be sure to let the students know how many people live in the household and use the various water appliances generating greywater.

•    Bring students back together. Share rainfall and greywater totals.  Emphasize the amount of water available to the site.

•    Compare this water income to potential water expenses or needs. For example, in Tucson, AZ, a 20-foot-tall native mesquite tree needs 3,000 gallons of water per year – how many such trees could be sustained by the building’s roof runoff? An exotic 16-foot-tall citrus tree in Tucson needs 8,000 gallons of water a year (and supplemental irrigation in dry seasons – think greywater) – how many such trees could be sustained on site by harvested runoff and greywater?

•    Optional addition. You could give the students one additional calculation to determine runoff coefficients (estimated percentage of water running off their various catchments and their different surfaces by using Box 2.4 in Rainwater Harvesting for Drylands and Beyond, Volume 1.


– The Muffin Tin and Sponge Models


Show how simple landforms can dehydrate or rehydrate our landscapes, while contributing to, or controlling, flooding.


See Muffin Tin Demonstration (first half of linked video)


OBJECTIVE – Show how cisterns can harvest on-site water and reduce flooding runoff, but harvesting water in the sponge of the landscape’s soil via water-harvesting earthworks with mulch and vegetation gives us the greatest capacity of water harvesting and flood control for the lowest cost.


See Sponge Demonstration (second half of linked video)



•    Now that we know how much water we have on site, which areas are going to receive more water?  (Students should observe areas near downspouts, etc as receiving more water.)

•    Where can we locate our catchment areas to start to manage the water as it moves through the site?  Remember to Slow, Spread and Sink.  (Students either sketch the site on paper or work together in small groups to scratch basins, berms etc. on the ground.)

•    Remember to think about stacking functions. Where are the human traffic patterns, can we use berms as raised paths in areas where people walk?  What other elements can be used for more that one function?


Once we begin creating our sponge, remember the “Feedback Loop.” Continually reassess your work.
•    What is working?
•    What is not working?
•    Enhance what is working.
•    Change what is not working.

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