Wednesday, July 31, 2013


There are so many things we take for granted, accepting that these things will perform as we expect and anticipate them to do. The telephone for instance. An airplane taking flight, a computer giving us information, a simple water meter. There are people who understand how these things work, but to many of us, the operations of these things are more miraculous than understood. I have solidly been in the camp of people who have never taken the time to learn what actually makes a thing work. Until now.

The PLUShouse design is at the end of the development phase, and we have submitted the project to Oakland for planning approval. Included in the submittal to Oakland is the design of the house and the landscape, as well as the design of the recycled grey water system and the rain water collection system. These water systems were designed by our water consultant, Design Ecology, based in San Francisco, California. These guys have been extremely helpful and patient in walking me through the design of the systems. All diagrams shown are from Design Ecology and are intended for the PLUShouse.

PLUShouse water systems design by Design Ecology

In very broad strokes, I will explain how these systems work.

There will be 3 distinct water systems in the PLUShouse:
1.        Municipal water system, for potable water and water used in sinks and showers.
2.        Grey water system, which recycles all water except food sink and toilet water, which will be used in irrigation and toilets.
3.        Rain water collection system, which collects rain water from the roof to be used for irrigation and toilets.

These three water systems are plumbed independently, but will have the ability to feed into each others' systems to satisfy the particular demands for water.

Municipal water system
 We take indoor plumbing and municipal-supplied water for granted, but indoor plumbing was extremely rare until the growth of modern cities in the early 19th century, when better waste disposal systems were installed to prevent disease. In 1845 the first screw-down water tap was patented, and indoor plumbing began to be installed in buildings in the mid-late 19th century.

women carrying water in Nigeria
City-supplied water originated in ancient civilizations to provide public baths, potable water, and drainage of wastes. Standardized earthen plumbing pipes appeared in the Indus Valley civilization by 2700 B.C. The Roman Empire had a vast system of aquaducts to transport water from far away, and used lead pipes to bring the water into homes, public wells, and fountains.

Roman Aquaduct
Roman fountain @ Villa D'Este
We now have more advanced technology and know not to use lead pipes to transport water. But our water can still come from great distances. Oakland water originates from several sources, much of it coming from the Mokelumne River in central Sierra Nevada. This water is stored in the Camanche and Pardee Reservoirs, then transported to Oakland via the Mokelumne Aquaduct. The water is then routed to each neighborhood and directed into each building, where it is piped to each specific plumbing fixture. 

After municipal water is used it is collected in sewer laterals that feed into a network of city sewers, where interceptors (large pipes) carry the water to a treatment plant in Oakland. Here it goes through primary treatment involving screening and settling out large particles. The water then moves to secondary treatment where organic matter is removed and the water is disinfected to remove any remaining bacteria. After being treated, the water is discharged into the San Francisco Bay.

Grey water system 
If a greywater system is installed in a building, all used water is separated into either grey water or brown water.  Greywater comprises 50% - 80% of residential "waste" water, and is essentially all water that has been used, excluding water from toilets and food sinks. A greywater system, such as the one we will be installing in the PLUShouse, recycles greywater for irrigation and toilet water.

The ‘elevator version’ of how a domestic greywater system works is as follows:
After water has gone down the drain (from all fixtures except food sinks and toilets), it is routed to a separate greywater plumbing system. The water passes through a pre-filter, and then enters a greywater holding tank. This tank can either be above or below ground, and is sized according to projected water usage. The greywater tank in the PLUShouse will be a 200 gallon tank (roughly 3x the size of a standard domestic hot water heater), and will be buried underground. When there is a demand for water by either the irrigation system or to fill a toilet tank, the stored greywater will be pumped through a series of filters, then enter the system requiring water. If there is not enough water in the greywater tank to satisfy the demand, water will come first from the rain water tank, then from municipal-supplied water if the rain water tank is empty. According to code, water can remain in the greywater tank for 24 hrs. If the water is not used within this time frame it is drained to the city sanitary sewer line. The brown water, which is not recycled, is directed to the municipal sewer system.

greywater treatment

Stormwater runoff is considered sewage, and goes to a separate facility. Certain cities, including San Francisco, have a combined system for sanitary sewer and sewage.

Rain water collection system
The third plumbing system to be installed in the PLUShouse is the roof water catchment system, or rain water harvesting system. Similar to municipal water and greywater systems, it has a very long history, beginning in the 3rd century BC with the farming communities in present day Pakistan, Afganistan, Iran, and India. Currently, it is common practice to use rain water for all water needs in many parts of the world. In California it is only legal to use rain water for irrigation and for toilets, although in Alaska, Texas, and Ohio rain water can be used in all applications, including potable water. It is mandated to install water harvesting systems in new residences in Santa Fe, New Mexico, and in the US Virgin Islands, as well as in many parts of Australia and other parts of the world with low precipitation.

Cudo system
The rain harvesting system we will be installing in the PLUShouse works in a similar manner to the greywater system, but the holding tank is much larger and there is no time limit for water to be held in the tank. The size of the tank is determined by the average annual rainfall in each specific location. Oakland has an average rainfall of 23.3” per year, which translates into a 13,000 gal. holding tank (100'x16'x6').  Instead of using a pre-fabricated water tank, we will be using a Cudo modular storage system, which is basically a series of 2’x2’x2’ plastic milk-type crates, secured together, wrapped in geotextile, surrounded by sand, and then wrapped in a polypropylene plastic liner. The crates act only to keep the shape of the ‘ tank’, which is really just a large bladder buried 2’ underground.

The short version of how rain water harvesting will work in the PLUShouse:
Rain water from the metal roof will drain to downspouts; run into underground pipes to the rain water tank location; pass through a pre-filter; then enter the rain water storage tank. (Water from the first rainfall of the season gets shed into the sanitary sewer system, as it has too much debris from the roof). A ‘smart valve’ tells the tank when water is needed, and the stored rain water is then pumped, or gravity-fed, from the tank, through a series of filters (backwashing carbon unit, reverse osmosis system or sand filter, UV filtration), and then to the desired location (toilet or irrigation). A valve determines if additional municipal water is needed to meet the demand, which is then supplied if necessary. As we are planting extreme drought-resistant landscaping, and anticipate using a total of 50 gal. of water per day, the greywater and rain harvesting systems should supply 100% of all non-potable water to the PLUShouse. What a wonderful way to go!

underground rain water tank

rain water filtration

Water is something we tend to take for granted, expecting it to miraculously come out of a faucet when we turn a knob, and continue to flow until we close the knob. This is not the case in many parts of the world, where water must be physically transported from miles away, and so is used with great care and thought. It seems wasteful to use water for a single application, when we can easily recycle this water for other uses. Design Ecology (our design consultant) will be canvassing Oakland to approve the usage of rainwater not just for irrigation and filling toilet tanks, but to use rain water as potable water and in all sinks, showers, and appliances. I will keep you posted on our progress.

next blog topic: how photovoltaic cells (solar panels) work

Lindy Small