Water Catchment

For minimum environmental impact and long-term sustainability, we look to rainwater as the primary source of water for any site design or community installation project, followed by reclaimed greywater and natural spring water (if available).  Because it is the result of natural distillation processes, rainwater is one of the most abundant, cleanest, naturally occurring fresh water resources on the planet.  Catching and holding rainwater locally onsite reduces the pressure on aquifers and municipal water systems.  Every gallon of water that is captured off a roof is a gallon of water that doesn't have to be chemically treated to drink.

We can increase the local moisture on any land by maintaining and cultivating healthy forests.  Although more research is needed, there has been evidence that forests on windward slopes and cross-wind ridges induce humidity, cloud formation, and rain. In Sweden and Australia where the effect of forested ridges on rainfall have been more closely studied, 40% of the rainfall has been credited to the trees. [1]

Onsite at the Center and through our workshops and community installation projects, we rely on a number of simple techniques for increasing, catching, storing and treating available water including:

Image courtesy of James Piers Taylor, http://www.naturewise.org.uk/page.cfm

Rainwater Catchments:  Water can be collected from most roof surfaces, although for thatched roofs, only some types of grasses should be used, namely coconut and anahaw palm, thatched tightly.[2]

Earthworks: Earthworks are techniques for shaping the earth for fortification and erosion control, to hold back water, and to provide support or protection from the elements.   We incorporate earthworks to capture and hold water high on the land. 

Some of the most useful earthworks for spreading and storing water are swales, ponds, dams, and diversion channels.[3]  Swales are long level excavations that catch overland flow of water, and allow surplus to infiltrate as groundwater recharge.  Swales can be accompanied by tree or vegetation plantings to avoid water-logging.  Orchids, fungi, and ginseng do better in swales in humid forests because they are humus rich[4].  Swales also make sheltered plating spaces on windy sites.  Small dams capture water to use immediately for irrigation and provide storage for use in periods of drought.   Diversion banks channel water away from valleys and streams and can be routed to connect to on-site dams and ponds.  Small walls across diversions can create mini-swales for specific planting sites.

These techniques, used together comprise a gravity-fed Keyline system, which can be used to “drought-proof” any land.  Fitting a site with earthworks for water storage on 10-15% of the land should be sufficient to eliminate fire, drought or flood threats.[5]  Areas that naturally absorb a minimum of 15% of run-off can be designed to capture and hold 100% of overland flow.[6]  Nearly any type dam is a cost effective method of capturing water if it is located on a slope of 5% or less.[7]  The most efficient dams maximize the ratio of dam length to height.  Dams that are shallow but long are the most efficient in terms of energy used compared with water stored.[8] Any dam site should be careful considered for soil type (clay fraction), grade (lower slopes have greater capacity), downstream infrastructure, and height (relative to areas of use).[9] Proper siting for dams is critical; a well-sited dam can impound 20-100 times the amount of water of a poorly sited dam.[10]

Bio-Sand Filters: When capturing water from natural sources, it is important to test the quality of the water and if necessary, to implement an on-site purification system.  One of the least expensive systems, is a bio-sand filter.  The medium for filtration is typically sand, but other small particulate such as rice husks can also be used.  There are both continuous flow and intermittent bio-sand systems available.  Continuous flow systems require a constant wastewater stream, and rank second to desalination in terms of physical, chemical, and pathogenic purification.  Household systems with intermittent water flow haven’t been researched as thoroughly, though they have shown similar performance.[11] 

Gravity-Fed Water Systems: Ideally the freshwater system will not require pumps.  Gravity-fed water systems are preferred for off-grid systems as they require no electricity, have fewer parts (such as pumps), and are simple to maintain.

Wind or Solar Water Pumps: Water pumps are required if there are points of use above the water source.  Two of the easiest energy options for pumping water are wind and solar.  Wind can be an economical solution if there is steady, moderate wind year round.  However, due to the lack of predictability on a day-to-day basis, wind could pose a problem for critical water supplies unless there is a large storage device, or backup pumping system.  Wind is most practical for a system that has a low water requirement and is capable of storing enough water for several days, or even weeks depending on demand.  

Solar is ideal for remote water pumps because the system can pump water all day long when the sun is out to fill a cistern that will be used at night.  This particular type of system has the advantage of not requiring a battery back-up, although it is significantly more expensive than wind pumps.