NOTE: Make sure you read the first three posts (in order!) before tackling the rest, or it could be confusing: Post 1 is Designing the future, Post 2 is Setting up the problem, and Post 3 is Estimating basic requirements.


Thursday, August 10, 2006

Water, water everywhere...

Just to get the designer wheels in your head started spinning, Peak Energy posted a good link to a story about a successful ground heat pump.

I have a little bit more to say about basic requirements as discussed in the previous post. Looking at Objective 2.1 (“The community will provide indoor plumbing adequate for four people.”), I’m starting to think that the driving goal (Goal 2) should be changed so that we can use it to address all the water management needs. This type of modification is common as Systems Engineering solutions are developed and I hope it shows you how fluid the design process is.

So, instead of Goal 2 reading “The community will have indoor plumbing”, how about “The community will provide adequate water supplies.” We’ll leave Objective 2.1 as it is, but add Objective 2.2: “The community will provide enough water to sustain four people.” Now that we fixed our goals and objectives, let’s define some requirements.

Taking some liberties with the data, the average human needs approximately 5 liters per day (lpd) for drinking, 45 lpd for hygiene and bathing, 20 lpd for cooking activities, and 3500 lpd for food production according to the Pacific Institute. (Very good link by the way.) Bear in mind these numbers reflect only the water “at the tap” – they take into account moderate efficiency improvements over the average American’s lifestyle and say nothing about recycling or help from local rainfall.

I will put these numbers into two categories: personal and agricultural, with respective values of 70 lpd and 3500 lpd. For the four-person community, this comes to 280 lpd for personal water and 14,000 lpd for agricultural water. This leads naturally to two requirements – “The community shall provide no less than 280 lpd of indoor water.” (Requirement 2.1.1) and “The community shall provide no less than 14,000 lpd of water for food production.” (Requirement 2.2.1)

Notice two things about these requirements: 1) They are wild-ass estimates and will surely be modified as your design develops and 2) they are intertwined with each other and their parent objectives. I could just as easily put Req 2.1.1 under Objective 2.2. Assigning requirements often comes down to intuition or preference, but remember that in the end every objective (for any project) must have at least one requirement. This ensures that every objective is met.

In future posts I will talk about planning for changes in your local water allocation due to global warming effects, aquifer depletion, or upstream pollution.


At 1:38 AM, Blogger James Samuel said...

If this blog is going to remain useful as a resource it is likely to need a certain functionality that doesnt come as an automatic feature of blogspot - categories.

An ability to categorise posts for easy searching and reference will be very hepful as it grows.

Searching for ways to do this will bring up lots of options, most of them quite complicated. I have used in the past but took it off my blog as it was unreliable and added a big overhead to page load time, making it unworkable for anyone who was not on a fast connection.

Maybe another reader has found a solution to this.

At 3:12 PM, Blogger PeakEngineer said...

Thanks James. I do have plans to add functionality as the blog grows. In the meantime (before I find a permanent solution) do you think a google site search would suffice?

At 8:22 PM, Blogger Big Gav said...

I live with just Google site search though Technorati tags are better - if you can be bothered with the overhead of adding them (for short posts its fine, but it doesn't work for my sprawling post style).

At 5:31 PM, Blogger inculcated said...

Some ways to mitigate water use, and to extend what is done with water....

Waterless Toilets

Grey Water Recovery

At 7:47 PM, Blogger Zachrey said...

I love this systems engineering approach to community desgin!

I'm Zac Helmberger and my wife, Nicole, and I live at the Greater World Earthship subdivision near Taos, New Mexico.

Greater World is a 633 acre subdivision that contains nothing but earthships (homes that provide all of their utilities using nothing but sunshine and rainfall). There are no water lines, sewer lines, gas lines, power lines, phone lines, etc. The only cop-out is propane tanks for cooking and backup water heating.

Private wells are not permitted on this subdivision! Thus all your water comes from the sky or you have it delivered for a reasonably small expense. That's the kind of game I want to play!

I have a website:

Regarding water use, my wife and I, combined, use about 24 gallons of water per day from our 3,600 gallons of rainwater cistern storage.

Let me know how I can contribute. I collect rainfall data and water usage data and am committed to continuosly increasing Greater World's ability to increase runoff catchment and storage for increased food and compost production.

Rainwater is filtered and used for washing and drinking. Water from sink, shower and washing machine drain into an indoor contained greywater planter. The toilets are flushed with the greywater and the reulting blackwater goes to a conventional outdoor septic tank. The effluent or excess water from the septic tank drains into a contained outdoor blackwater planter where trees and crops are grown. Any left over blackwater then drains into a conventional drainfield. I love it!!

At 1:23 AM, Blogger bytestyle12 said...

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Saturn Aura Air Conditioner Compressor


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