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Does using grey water to water one’s plants affect their growth?

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Picture of Does using grey water to water one’s plants affect their growth?

Scientific explanation of grey water's affects on plant growth. Quick and easy to follow.

 
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Step 1: Background Information:

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Today we are faced with two significant issues in society: the overuse of the finite supply of water in the world and the cost of living. Many households save both water and money by recycling grey water on their garden. This means watering ones garden with old dishwashing water, shower water or laundry water.

However, does the soapy water negatively affect the plant’s growth and development. Some sources say that “plants have been scientifically proven to grow better with grey water” [1] . However some other sources suggest that it could harm the plant and that normal clean water should also be used.

“the potential harm is less to the plants than to the soil, with its complex bacterial and fungal make-up. Recycled soapy water (‘grey’ water) is perfectly usable for plants, but I would not use it exclusively. Rotate it with ‘clean’ water on an alternate basis and, as with all watering, direct it at the roots rather than the foliage.” [2]

[1] http://waterwisesystems.com/learn-more/why-a-grey...

[2] http://www.dailymail.co.uk/home/gardening/article...

Step 2: Aim

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To find out whether using a solution of detergent and water to water plants will negatively effect the growth of that plant.

Step 3: Hypothesis

The more detergent used whilst watering the beans, the less these beans will grow. All the beans will show some growth.

Step 4: Equipment

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- 9 Sauces

- 18 Lima Beans

- 72 cotton wool disks

- 20mL Syringe

- Cold Water

- Washing Detergent

- Ruler

Great stuff! I'd def try it again with more representative concentrations though. I water seedlings myself with grey water and it seems to be oh Kay. Not only is there detergent in my water – quite a small amount, but also a small amount of urine! Voted.
Bunchgrass5 months ago

Consider that plants, even germinating seedlings, need oxygen (and water) to carry on the process of respiration necessary for growth. The soap level may have acted as a surfactant, keeping any oxygen from being available for the bean seed. Just a thought.

daveand56 months ago

Years ago in Texas when potassium wasn't removed from everything, grey water was emptied from the washing machine onto the backyard canna lily patch. we also had canna's in the front yard, these grew to about 4 ft tall. The ones receiving the grey water grew to over 12 ft tall. Washing detergent is different than dish soap, even back then. Maybe you should do this again using washing detergent.

ysaks (author)  daveand56 months ago
interesting ... Maybe I will do another experiment
billbillt6 months ago

Very well done test...

ysaks (author)  billbillt6 months ago
thanks
daveand56 months ago

Oh and almost forgot, dish soap is used almost universally as a quick and cheap wetting agent for applying liquid fertilizer and weed killers, just a few drops in a gallon effectively improves the coverage and 'wets' the sprayed items so much better it can be seen with the naked eye.

daniellakey6 months ago

Excellent idea for an experiment. The only comments I would have about your procedure would be the concentrations of soap you are using. The question of the experiment is about grey water effect on plant growth. I'm not sure about how much soap they use when doing a load of laundry at your house, but I know at my house we are not using a couple gallons of soap per load of laundry, but that is the kind of concentrations you mentioned in your experiment. In your 10ml experiment you are talking about a 50% concentration of soap, and on your 5ml experiment you are still dealing with a 25% concentration. Still much much higher concentration than ANYONE would routinely use for household use.

The reason grey water is thought to be beneficial to plants is due to the phosphate content of many soaps, which is one of the 3 major plant nutrients that are included in commercial plant fertilizers. The other two being potash and Nitrogen.

But just like putting too much fertilizer on a plant out in the garden will burn it up and hinder growth, the same thing here. I would think you should try the experiment again, except this time instead of 25 and 50 percent concentrations, try something closer to 1 percent concentrations or even less.

Also, you need to make sure that the soap you use does include phosphates, because I believe there is a pretty strong push on now to reduce the amount of phosphates used in soaps due to the effects of high phosphate waste water has on waterways when discharged, causing overgrowth of algea in the water, caused for the same reason that your plants like the grey water.

Anyway, with all of that said, I think it is a great idea for an experiment and I believe you will get some different results with those changes in concentration.

ysaks (author)  daniellakey6 months ago
Thank you for taking the time for reading and commenting.
Misac-kun7 months ago

Excelent work!

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ysaks (author)  deleted_account7 months ago
Thank you
omnibot7 months ago
A well performed experiment.Yay!
lemuries7 months ago

This was a very interesting read, and I am very grateful you shared your results with us. I think your methods were excellent and I was also surprised by the results you weren't expecting. Thank you for sharing this with us!

ysaks (author)  lemuries7 months ago
Thanks for the feed back?