Laura Allen

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since Mar 31, 2015
Laura Allen is a founding member of Greywater Action and has spent the past 15 years exploring low-tec sustainable water solutions. She is the lead author of the San Francisco Graywater Design Guidelines for Outdoor Irrigation, and authored The Water-Wise Home: How to Conserve and Reuse Water in Your Home and Landscape (Storey Press, 2015). She has a BA in environmental science, a teaching credential, and a master’s degree in education. Laura leads classes and workshops on rainwater harvesting, greywater reuse, and composting toilets. Laura has presented widely on greywater reuse, including at the Water Smart Innovations Conference, Bioneers, California Environmental Health Association conference, and California Landscape Contractors Association conference. She’s participated in state greywater code developments in California and Washington State and was on a committee to write a draft composting toilet code for IAPMO. Laura was featured in an Ask This Old House episode on greywater and was the 2014 recipient of the Silicon Valley Water Conservation Award of Water Champion.
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Recent posts by Laura Allen

David Hernick wrote:This thread reminded of something I saw on Penny Livingston, here is a link:
The picture says it is a grey water pond for ducks, but the article does not go into much detail on the pond. ...

Just want to offer a little more info on the greywater pond: I visited one of her ponds, at RDI, and it was mostly a rainwater-fed pond with just a small fraction of the water from filtered greywater.
3 years ago

Peter VanDerWal wrote:I would not bother trying to use either grey water or rain water for your toilet, it would be a waste of time and resources.  Anything that goes down the toilet is gone for all practical purposes so why bother using rain water?

Rain water is an excellent resource for watering your garden, unless you can collect so much that you can't use it all on the garden, why waste it anywhere else?  The same goes for grey water.

Until you get to the point where you have an abundance of rain/grey water and can't use it all in the garden, it's pointless to try using it anywhere else.  Think about it, if you want to use it in the toilet you are going to have to build filters etc. which will require time and materials (money) then you will have ongoing maintenance of those filters (more time and resources), plus you will have to add new plumbing, seperate from your existing plumbing, to route this water to your toilets.  Either that or fill your toilets from buckets (more time and resources).  After you go through all of that, what do you gain?

Good point! You should first calculate how much irrigation demand you'll have and then see if you can match it with greywater and rainwater. I also wouldn't pursue a rainwater-to-toilet system unless you have more of it than you need for irrigation.
3 years ago
Hi Daron,

It sounds like you're planning to get this permitted, in which case the local regulators will have a lot of influence on the specific design.

The filtered water will be similar to any septic effluent, and there are lots of examples of distributing that water into the landscape (not just a leach field).

I would ask them what methods they allow for distributing septic effluent, and if you don't like the options then ask if they'd allow an alternative.

Depending on your goals with the system traditional distribution methods may work just fine for you.

Your post made me wonder why you are considering redoing your septic system? Is it failing?

Best of luck with your system!

3 years ago
Hi Francien,

Sounds like you have the perfect site for a gravity flow greywater system!

And it sounds like a simple type of greywater system would be a good match for your home/landscape.

With a simple greywater system the only filter you need will be in the landscape. You'll create what are called "mulch basins," shallow depressions in the soil that are filled with wood chips, this is where you'll direct greywater to be filtered by the wood chips. The mulch basins act as a filter and a sponge, and also spread out the water to cover more of the root zone of the plant.

I describe how to design and install a few systems that may work for you in my book, Greywater, Green Landscape. Unfortunately it would take too much text and images to post how to do it in this forum, so I'll just give you a few more resources to seek out. I'm part of an organization called Greywater Action and we have a bunch of on-line resources including webinar and downloadable manuals. In particular, I'd recommend you view the webinar about branched drain systems,%20Branched%20Drain%20Systems%20and%20Greywater%20Irrigation%20in%20Arid%20Climates

Using rainwater for toilet flushing does require filtration. You'll most likely want to get a professional involved since you'll need to clean the water and make sure you've adequately protected the potable water supply. An improperly design system could create a "cross connection," where non-potable rainwater (imagine animal feces on the roof being flushing into system) is unintentionally mixed with the potable supply, contaminating the potable water.  One form of protection against cross connection is to just have a separate system you connect to, and when the tank runs out you manually switch over to the municipal supply. Other options include using an air-gap and refilling the tank with the municipal supply, or using a reduced pressure principal device. Your local regulators will most likely require one method or the other; you should check. The rainwater will need to be clean enough so grit and debris don't get into the toilet tank and interfere with the flush mechanisms.

Here is an excerpt from my book The Water-Wise Home that give you some specific details:

From The Water-Wise Home:

Sample Treatment Methods for Indoor Use of Rainwater

Specific filtration and disinfection requirements are determined by local regulations and installer preferences, but here are some common treatment methods for different end uses:

▪ Filtration: Minimum 50-micron sediment filter (prevents grit from interfering with toilet valves)
▪ Optional: Carbon filter to address any color or odor issues
▪ Permitting agencies may require 5-micron filters and disinfection

Hope this helps!
3 years ago
I should add to my previous post, that the best type of ecological disposal system for greywater would be a constructed wetland or self-contained planted area (like an evapo-transpiration bed). This method allows greywater to be used, and used-up, without any impact on the natural environment, and is important to use if the site is near any water ways.
3 years ago

Elizabeth Rabeler wrote:

Hi Laura, we would like to fill the pond with freshwater and then use greywater from our house to keep it full and refreshed. I am thinking of a small pond, nothing too grandiose- just enough for 7 ducks to enjoy.

Hi Elizabeth,
I would not recommend you fill the pond with greywater. In the past I've had a similar system, but, at the home-scale, I wouldn't make it again.  I'll post a short quote from my book which speaks to this type of system:

From Greywater, Green Landscape: Though technically easy and also beautiful and fun, treating greywater
for a backyard pond is not something I recommend. If your goal is to save water, a greywater pond isn’t the right choice. The quality of greywater is unsuitable to fill a pond; it must be filtered by wetland plants first (unless you want a pool of disgusting, stinky greywater). Thirsty wetland plants not only use water, but they also remove nutrients and organic matter from the water, which your garden could benefit from; less greywater flows out of the wetland than in.

A water-wise choice for anyone with both a pond and a landscape is to irrigate with greywater and fill the pond with freshwater (or rainwater), bypassing the need for the water-loving wetland filter. Separately, greywater ponds epitomize the concerns of the regulatory world. Their list of potential hazards includes: drowning risk for children, potential for direct contact with the water, mosquito breeding grounds, and possible overflow to a neighbor’s yard or storm drain. Ponding greywater is prohibited by even the most lenient codes.

If you're interested in using greywater to benefit the ducks, I'd recommend using it to irrigate plants the ducks love to eat, or growing a shade tree over the pond you create.

Good luck with your system and the cute ducks!
3 years ago
I don't see anything wrong with the system you describe. You're right, it would be a different situation if it was close to a drinking water well, creek, river etc. because then the nutrients in greywater would be pollutants and cause algae to grow. If the area was really boggy, with a high water table, then greywater could get into the groundwater, which is not something you want. The water will be purified as it travels through soil, so you should have a few feet of separation between the discharge and groundwater level.
3 years ago
I'm not sure I understand your idea. Are you filling the pond with freshwater, and then wondering what to do with the "greywater" you get after they've gotten it dirty?
Or, are you thinking of filling the pond with greywater from the house?
3 years ago
Hi Chris,

This is a concern many people bring up.

Here are a few thoughts:

1) For the record, this concern should be brought up to anyone proposing reduced flows with Water Sense standards, plumbing code changes, rebates for installing low flow toilets, etc. I feel that greywater gets this question disproportionately

2) We have an aging sewer system that needs attention, and we need to make it work with modern flows, which will use lower flow fixture.

3) New sewer pipe are required to be sized based on outdated flow estimates, resulting in problems with low flows. We need to change flow rate estimation equations to match modern fixtures.

4) I touched on this in my book, Greywater, Green Landscape, here is an excerpt:

"The Bigger Picture
What would happen to the entire municipal sewer system if lots of people reused greywater? Massive sewage clogs? Probably not. In the Study of the Effects of On-Site Greywater Reuse on Municipal Sewer Systems (2011; see Resources) researchers used hydrologic models of the sewer system to identify levels of flows and pollutant loads throughout the day. They found the sewer system operated with large fluctuations in flows, with two major peaks occurring each day (morning and evening). Reusing greywater would have the largest impact on the system during these peak flow times (imagine lots
of morning bathing water going into the yard instead of the sewer). Widespread reuse of greywater would reduce the peak flows but would have almost no impact on the system during the current lowest-flow times of the day (when toilet flushing is the major source of water in the system).
Because the sewer system currently operates at these low-flow times, and these flow rates would not be affected, researchers concluded that widespread reuse of greywater should not increase blockages. In fact, they hypothesized that sewer systems could experience positive effects from greywater reuse with an increase in capacity."

3 years ago
Yes, the book does address slab-on grade construction. Your options are more limited than people with crawlspace, but you do have options!
5 years ago