Waterharvesting's Blog

Getting the most out of gray (grey) water and rainwater harvesting

Posts Tagged ‘garden

Understanding Irrigation Efficiency

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Introduction:

It is tempting to believe that whichever way you have decided to reuse rain or graywater, that you are saving at least as much water as you are placing in the garden.

Over the years, several methods of reusing graywater, based on mulch basins, have become popular. The sad fact is that simply placing graywater into a mulch basin surrounding a tree (a mulch basin is basically a big hole around the tree covered in mulch) isnt very efficient at all.

If you put 10 gallons of water into this mulch basin, it will have the same effect as using 5 gallons of tap water into the hole at a more measured pace. Yes you have saved 5 gallons of tap water (because you ddn’t need to supplement with tap water), but you could have saved 15 gallons of tap water by using the 10 gallons of graywater to greatest effect.

The following discussion is focussed on graywater reuse, however the same principles apply for rainwater reuse.

Detail:

These are the commonly accepted methods of reusing untreated graywater:

  • Buckets
  • Branched Drain (or similar)
  • Laundry to Landscape
  • Gravity Dripperline
  • Pumped Dripperline

Before going in to the pro’s and con’s of each method, the concept of how much water is actually saved needs to be understood.

If you put 10 gallons of water in one 4′ hole in the ground every day, you have not saved 10 gallons per day. In Tucson, Arizona, that hole only needs 12 gallons for the whole of July for medium water use plants.

If this was done daily, then 300 gallons has been irrigated over the month, instead of the required 12 gallons.

The actual amount saved is 12 gallons. The irrigation efficiency is 12/300 or 4%.

This may sound extreme, but I have seen quite a few branch drain systems set up this way (the rest of the water goes down into the subsoil and is wasted, unless trapped by clay in which case the roots of the plants may rot).

So while on the surface some methods may appear to be very inexpensive for the amount of water diverted, the amount of water actually saved needs to be reviewed.

Irrigation Efficiency Rates for Different Methods:

Irrigation Method Efficiency
Buckets 50%
Branched Drain 30%
Laundry to Landscape 40%
Gravity Dripperline 90%
Pumped Dripperline 90%

The efficiency rates listed for branched drain and Laundry to Landscape methods are extremely generous, based on absolute best practice installation methods by highly experienced installers.

Cost / Benefit Analysis of the different methods.

After applying the irrigation efficiencies of the methods, determining how much potable water is no longer needed to irrigate the garden, these charts can now be presented.

If you would like the maths behind the following charts, please contact us via the contacts page for more information.

cost_v_saving_water_reuse.jpg

Cost vs Gallons of Potable Water saved over 5 years

Assumptions:

Paid labour has been used for installation of all methods except for bucketing of water. A small amount has been added to the bucketing methods, for 1 chiropractic visit (this isnt a joke, it’s an onging issue in Australia).

While voluntary labor (you) can be used to reduce the cost, the efficiency of Branched Drain and Laundry to Landscape methods will typically halve. Those interested in installing their own Branched Drain network should go to our videos page and review the branched drain installation video (8 minutes)

cents_per_gallon_water_reuse.jpg

Cost per gallons of water saved over 5 years use.

This chart illustrates how Dripperline irrigation is far more cost effective over 5 years (at about 0.5 cents per gallon) than even Laundry to Landscape at about 2.5 cents per gallon.

For more information about the pro’s and con’s of different graywater re-use methods, go to part 2 of this article http://www.besthomewatersavers.com/pages/Different-ways-to-reuse-graywater-%28part-2%29.html

Water Harvesting – it’s more than just Rain

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This blog is about extending the concept of water harvesting from simply rainwater harvesting, to harvesting all the water across the home.

Rainwater is extremely valuable, especially as water utilities start raising the price of water to cope with infrastructure upgrades required now, not just the future.

Relying on rainwater alone to help reduce water consumption in the home is risky business (unless you live a cool, moist environment). Over 60% of water use in the average American home is in the garden, and rainwater collection (and storage) can help supply this water.

However if you live in an area that has rainfall for 6 months of the year, and dry for the remaining six months, relying on a rainwater harvesting system can be very expensive.

Lets say your garden area requires 3,000 gallons of water per month for irrigation. Lets assume you have a six month dry period (It could be worse – San Diego has a 9 month dry period).

To ensure garden water supply from rainwater harvesting alone, the tank / cistern would need 6 x 3,000 gallons, or 18,000 gallons capacity.  Apart from the expense involved (many thousands of $$), tanks / cisterns this size require a huge area, and land is expensive.

So the purpose of this blog is to explore the many different methods of water harvesting, such as rainwater harvesting, graywater (also know as gray water, greywater and grey water) re-use, reclaimed water, alternate water supplies; and most importantly place these methods into the appropriate context.

I promise to be straightforward and forthright in this blog. Water politics is not just confined to America, it is a world-wide phenomenon.

Water is a vital resource, second only to air, and as a result is big money. Vested interests include (but aren’t limited to):

– Water Utilities / purveyors
– Water fixture manufacturers
– Water treatment manufacturers and irrigators
– Water re-use designers and manufacturers (be kind – I am one of these!)
– Environmental quality jurisdictions
– Federal / State / City / Country code officials, planning consultants, and inspectors
– Plumbers / irrigators / landscapers

– and the most important stake holder of all; YOU.

I now have over 7 years of water re-use experience in Australia, and 2 years experience here in the US – at local, state and federal levels. Based on what I have learnt so far, the challenges facing America far outweigh those experienced in Australia.

The water / money relationship is much bigger in the US, and the stakeholders above all recognise the issues are serious, they just havent worked out how to work together on it yet. It is likely they will not come to agreement willingly, after all money is involved.

In the end, YOU, the consumer of water will ultimately drive how water is delivered to your home, how much you will pay for it, how you will use it (and re-use it, hopefully over and over again). You may not have control over how much you pay per gallon for water supply and sewerage disposal, but you will be able to control how much you potable water you consume.

Of even more concern to the regulators, is that YOU also decide whether to adhere to codes after the house is built, and they know code violations are everywhere. A pragmatic approach would be to develop codes that were sensible to the typical consumer, or change core infrastructure to cope with code violations.

In future posts, I will provide examples of how pragmatic solutions are rarely, if ever, found in the water regulation industry.

This primary focus of this blog is to raise awareness of what can be done, and what the impediments are.  But it would be stupid of me not to promote two of my websites:

To read more about rainwater harvesting vs graywater go to: http://www.besthomewatersavers.com/pages/Rainwater-Guide.html

Written by Waterharvesting

June 12, 2010 at 7:40 am