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A relative is rebuilding his bathroom. Since he has a garden and he is all about "thinking green" he was wondering if he could use the shower water (or any other) in any way, like water plants.

I found the idea interesting when he told me and we googled a bit around to see what solutions there are. We found many ways of saving water, but none to reuse. I assume one cant just use it directly due to the soap and other chemicals. Is there something that its practically doable in order to be able to reuse this water safely?

The idea is to save money, but above all to avoid wasting water.

  • 1
    I don't know if shower water (associated detergents) are any different, but I'm pretty sure you can use your washing up water (containing regular washing up liquid) directly in the garden. In fact, as I understand it, this is a good treatment for your plants if you have blackfly, etc. – MrWhite Oct 12 '15 at 16:31
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The search term you are looking for is probably "greywater" (or graywater.) Basically non-toilet (watercloset) waste water.

There are two aspects - one is legal and varies by location, the other is practical and does not, so much.

The legal aspect essentially comes down to whether your local jurisdiction prohibits or allows use of graywater (rather than requiring that it go into the sewer), and any specific regulations/rules you must follow to use it in the jurisdiction. Some places essentially limit you to the output of the kitchen sink, for fear of tiny amounts of bad things that might be in laundry or shower water; others do not. Most have fairly strict rules to prevent the cross connection of sewage and greywater lines.

The practical aspects tend to have to do with things like filtering it through a reed bed or similar wetland plant-filter before making further use of it, which deals with the soaps, toothpaste, etc. Any practical permaculture book tends to have a few diagrams of this sort of thing in it. How practical this for a given house/garden depends on available space and topography.

If you are not in a terribly dry region, storing rainwater may be easier to manage than diverting and filtering greywater.

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You can pipe it to a tank and use it to flush lower-floor toilets. Apart from that, in most areas it isn't cost-effective to try to reuse it.

In NYC, fresh water is roughly $.01/gallon, and shower heads emit 1.5gpm. So the water savings from a 5 minute shower are worth perhaps 3 cents; this doesn't even pay for the piping necessary to recycle it.

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    I'm impressed that anyone has the strength of will to get out of a shower after 5 minutes. I'm doing well if I can keep it down to 10. – keshlam Oct 13 '15 at 3:48
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    From a cost perspective you're right. One needs a lot of water to pay for the project. That's why keeping the cost low is important. In other hand there are other relevant factors, like saving water, that drives him. – nsn Oct 13 '15 at 7:58
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    It is far more effective to put in a low-flow showerhead and to take shorter showers than it is to try to build your own grey-water recycling system to handle perhaps 20 gallons/day... – gbronner Oct 13 '15 at 16:15
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    While water tends to be very inexpensive, there are times and places where watering your garden or lawn with it is prohibited by law or custom, such as California, or Vancouver, BC in the late summer. In these circumstances, greywater may be an economical alternative. In any case, I found a lot of information by googling for greywater. – user19474 Oct 13 '15 at 17:17
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Another Green option may be one of the systems that tries to recover heat from wastewater, rather than or in addition to separating greywater and septic drains. I've seen heat exchangers advertised, but have no information about whether they're really cost-effective.

  • That's exactly what I was thinking, I've seen products advertised like shower-save.com and ecodrain.ca - I've not tried them or seen independent reviews or anything, though. – rjmunro Oct 13 '15 at 16:44
  • I've tried to investigate this for my own usage - a heat exchanger between the waste pipe and the incoming cold water. It won't save any water, but it will use a bit less hot from the cylinder. I never found a useful item, but the concept would be two radiators intertwined so the waste water takes the chill off the incoming cold. The main risk is blockages of the wastepipe due to hair going down the drain, which would be mitigated by having a long "water jacket" heat exchanger with a straight pipe through the midde. – Criggie Oct 13 '15 at 21:46
  • @Criggie I actually know someone with a patent for a highly optimized system like that. The system is not commercialized yet though. It's still in industrialization phase and I think they are actually delaying the process for some economical reason. – nsn Oct 14 '15 at 9:39
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I have reused bath water.

A standard crib sheet will fit perfectly over a standard oval 2x2x4 stock tank. Have a friend help you wrap twine around the stock tank before you put the crib sheet on, so the weight of the water won't make the sheet collapse into the tank. Pass water through the sheet to filter out most of the suds etc. The resulting water looks quite clean, especially if you let it settle.

If it sits too long, it WILL get gross. Use your nose and your own good judgement.

I put mine in a place to catch water from my rain gutter too.

My plants don't care, and the police certainly don't.

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There are several considerations here:

What is the shower's flow rate? Will the plants be flooded and die due to daily showers?

What are the ingredients in the shampoo/conditioner/body wash/soap? Are they environmentally friendly?

If this water is being used to water a garden then do you really want the chemicals from the soaps making it into their stomach?

Maybe your relative plans on simply showering without soaps? This sounds like the healthiest and most "green" solution.

Not sure what kind of work your relative does but I know that I can get pretty greasy when working on a car. I definitely see black/gray water running down my drain for a few minutes so I don't want that in my garden.

And finally, like others have said, is this legal?

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You can also wash your clothes with it. Gray-water (which is already sudsy + detergent you add) for the first cycle, fresh water for the rinse cycle. I believe there was an episode of "This Old House" (here in the US) that did that for a home owner. Very manual intensive though, home owner had to manually switch between collected gray-water and fresh water sources.

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Salt buildup in the soil and killing the microscopic eco systems present (vital) in the soil itself would appear to be the major barrier to reusing shower water in the garden. Plants themselves may tolerate some (biodegradable) soaps or detergents, but if the health of the soil itself is damaged, plants will suffer in the end.

This was a helpful link: http://ecologycenter.org/factsheets/greywater-cleaning-products/

I have often wondered about the plausibility of fitting a valve to kind of 'switch' drains (regular and 'clean'). clean in this case being the water used before its used. By that I mean; before it gets soapy or dirty - all the gallons wasted while waiting for the water to get hot. Even then, when you first step into a shower, you spend an initial amount of time just enjoying getting wet - no soaps involved. Maybe the same for some after the soaps are rinsed away. This water is as close as can be to regular clean water, its just touched the air between the sprinkler head and the drain!

If the ultimate aim is to reduce waste water, then a shower clock can help cut down time spent in the shower - and a lower flow rate shower head will also limit the amount of water used. These two alone will massively limit overall water use/waste. Final tip (I know its kinda off topic, sorry), turn off the water while getting soapy!

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