What is the best sustainable water option for irrigation? Well (pun intended), it depends on where you live and whether you are building a new or retrofitting an existing irrigation system. But first let’s review sustainability.
What is Sustainability?
There are 3 basic pillars of sustainability which must be considered and kept in balance:
Sustainable Water Source Options
• Potable – traditionally the “go to” source for irrigation water. Metered, getting more expensive and for the last 100 years a fairly reliable source for water.
• Fresh – water from a well, pond, river or creek. Fresh water is a great option when available, legal to tap and not being litigated in the Supreme Court.
• Reclaimed – “toilet to not quite tap”, but generally treated enough to be good enough for plants, if they can tolerate the high level of dissolved salts.
• Harvested – rainwater from roofs with minimal contact or storm water (rainwater that has run across the ground). The best water for plants is Mother Nature’s rain. Rainwater is free and plants love it, but it is not readily available when needed. Irrigation is needed most during the warmer months in the growing season when rain is intermittent at best. Storm water is good, but in the process of flowing across lawns, roads and parking lots storm water picks up pathogens which need a little treatment before people can me exposed. Again, there are legal considerations in a few western states, but times and laws are changing.
• Recycled – gray, A/C condensate, process, foundation subsurface drainage. These water options are being utilized more and more in new construction projects and especially in large, water intensive, manufacturing facilities.
Sustainable Water Criteria
• Quality – has to be good enough for plants and safe for people to be exposed to. Salts are detrimental to plants while pathogens are not safe for people.
• Quantity – irrigation uses a lot of water. An “average” 30 GPM commercial zone running for 10 minutes will use 300 gallons. If there are 12 zones, each time the irrigation runs over 3600 gallons are needed. Many properties have 2 – 3 times this requirement.
• Reliability – will the water be there when the plants need it? i.e. In the desert, rainwater is not a reliable source for irrigation water and in some drought stricken areas water restrictions do not leave enough time or enough days to apply the required supplemental water to the landscape.
• Embedded Energy – how much energy is used to treat and distribute the water to the irrigation system. In the case of potable water the embedded energy is quite high.
• Storage – goes hand in hand with quantity of water. In an upcoming post we will explore where 1,000,000 gallons of storm water is stored below ground, treated and used as a sustainable water source for an irrigation system.
• Carbon Footprint – some water sources may have a high initial carbon footprint, but in the long term have a low carbon footprint and vice versa.
• Economic – there is a huge variability in the short and long term economic impact on the various sustainable water options.
• Social – another variable depending on location i.e. well water used to provide a social and legal pass when it came to water restrictions. However, as the water stress in aquifers continues to build, wells may have a negative social connotation…especially if your deep well sucks your neighbor’s less deep well dry.
BACK TO THE QUESTION: “What is the best sustainable water option for irrigation?”
The Sustainable Water for Irrigation Table at the top left is a hypothetical ranking for sustainable water options and criteria. 5 points were assigned to the best options (green), 1 point was given for the poor options (red) and 3 points were allocated for everything else (black/gray). Based on this methodology, surface water is the most sustainable, followed by rainwater and a three way tie for third with gray, foundation and process water. Each site has different variables, so each chart will vary and the most sustainable water source for irrigation will change. One common consideration with substantial impact is the storage component. Whatever your specific conditions are, we hope you will think more about the best sustainable water option.
This post was inspired by the Sustainable Irrigation Webinar Series – “Green” Irrigation Systems presented by Brent Mecham with the Irrigation Association and sponsored by Hunter Irrigation and Ewing. If you liked this post about sustainable water for irrigation please leave a comment, share it with a friend, check out my previous posts , follow me on Twitter @h2oMatters and check out water stories I am reading on Flipboard: