Our waste water is largely just that—waste—but the push is on to put it to use

SINCE THE industrial revolution, and possibly going even farther back along the winding road to modernity, the children of every generation have been scolded for their wasteful habits.

To drive home the point that comfort and abundance should not be taken for granted, stories have been told about the amazing frugality of our ancestors, and there is a whole sub-genre related to water conservation.

We’ve all heard about the days when bathwater was shared by the children in the family, according to a pecking order which made the youngest sibling the last one to climb into the murky, tepid tub. I recall being told about the way my grandmother reused the wash water, laundering whites first and working her way down to the barn clothes, by which time the water must have been positively turbid.

Whatever its actual colour, today it would be called “grey water.” The term refers to water previously used for washing, as opposed to water that is flushed down the toilet with human waste, which is known as black water—or, more commonly, sewage.

Our thrifty forebears reused grey water for washing, primarily because it was hot (or at least warm), and they had devoted considerable energy to heating it. These days, most of us would take a dim view of washing with used water, but there is a movement to put grey water to use before sending it back out into the environment.

Waste not

If you have travelled south of Texas or east of Greece and wandered a little off the beaten path, you have probably encountered that most basic form of improved sanitation: the pit toilet.

In societies where safe drinking water is a precious commodity, the idea of using it to dispose of human waste must seem truly bizarre. Water is a fundamental human need, and there is no resource we can turn to as an alternative—but we on this continent are profligate in our consumption of water.

Today’s low-flush and dual-flush toilets have helped to reduce our wasteful water consumption, but we still flush away vast quantities of high-quality drinking water. By some estimates, toilets account for up to 30 per cent of our household water use.

Strategies for grey water usage tend to focus on water conservation by recycling what goes down the drain and directing it to uses that do not require pristine potable water. Since toilets do not actually require water that meets potability standards, they are a perfect application for recycled grey water.

The simplest application involves installing a toilet with a small, built-in sink, so the waste water from hand washing empties into the tank—to be used for the next flush. These models are common in some developed countries that have been forced to conserve water, such as Japan and Australia, but they are not yet widely available here.

Water used for washing dishes is considered grey water, but it’s not the best choice for recycling, because it contains food scraps as well as grease. Laundry water has its own complications, due to the presence of lint, detergents and contaminants ranging from fecal matter from cloth diapers to chemicals shed from soiled work wear.

Water from the shower or tub drain may contain hair as well as traces of soap and shampoo, but, generally speaking, it is relatively clean. And since the quantity of water from the shower tends to be a close match to what is needed for toilet flushing in a household, this is considered a good basis for a residential grey water recycling system.

There’s an element of common sense with this application: the shower drain is routed to a storage reservoir in the basement, solids are filtered out, and a dedicated pump delivers this water to the toilet. (Any overflow from the reservoir is directed to the sewage pipe.) The technology involved is not terribly sophisticated, and most of us would not be troubled if we noticed a bit of shampoo lather swirling around in the porcelain bowl.

Water standards

To meet building code and health requirements, grey water recycling systems actually have to be quite complex—you must have two separate distribution systems (clean drinking water cannot meet grey water), filtration systems must be in place to remove solids, and home piping must be carefully labelled and identified—and the equipment required to meet these standards can make grey water systems expensive.

For example, Health Canada has developed a detailed set of guidelines recommending that grey water be treated to remove pathogens, either with a UV system or chemical additives such as chlorine, and CSA standards exist for the design and installation of non-potable water systems. This might seem like overkill, given that the water is only being used to flush toilets, but early pilot projects demonstrated that untreated water in the reservoir is extremely hospitable to microbial growth, resulting in odour problems—as well as health concerns.

The guidelines also say there must be a provision to supply fresh water to the system automatically, in case there is insufficient water from the shower drain to meet toilet demand. And—because of regulatory anxiety about this kind of interconnection between grey water and potable water systems—an approved backflow prevention valve must be installed as a fail-safe precaution against contamination of drinking water.

Installing a complete grey water system of this kind, including the electronic controller, could cost several thousand dollars, or even more if the system has to be retrofitted to work with a home’s existing plumbing.

As with first-generation solar panels or any other new conservation technology, there have been a few early adopters who are willing to pay the price, for conscientious reasons or just because of their wonkish interest in green building. But most homeowners will not invest in conservation measures unless there is a financial payback period of less than 10 years, and the economics of grey water recycling aren’t there yet.

Making economic sense

This is expected to change as new systems hit the North American market; they will likely be cheaper, more reliable, and require less maintenance. But beyond cost, the need for regular servicing of grey water systems could be a deterrent at this point.

In the meantime, there has been limited movement toward “dual plumbing” in new home construction (along the same principle as “solar ready” design), which would significantly reduce the cost of installing a grey water system in the future. It is increasingly common to see the purple pipes that signify grey water, clearly marked as “non-potable,” to avoid any possible mix-up by contractors or do-it-yourself plumbers at some point down the road.

Most proponents of grey water recycling in Canada have taken a more centralized approach, targeting larger sources of waste water. Currently, grey water recycling looks most attractive for multi-unit buildings, where a centralized, large-capacity system can achieve some economies of scale. This is especially true for hotels, where guests tend to indulge in extravagant bathing practices.

Grey water in the garden

The other possible use for recycled water is irrigation, though this remains a grey water grey area. There are probably still quite a few homes in rural areas of Atlantic Canada where grey water just trickles into the backyard or into a “French drain,” (a trench lined with gravel).

However, stringent regulatory barriers to this sort of application exist in most jurisdictions in Canada, where regulators are more inclined to view all grey water as potentially harmful to human health. An outdoor grey water spigot would have to be protected by lock and key, and clearly identified as non-potable. Apparently, we are so accustomed to the luxury of abundant clean water that any unmarked tap could be seen as a source of refreshment for thirsty passers-by.

This kind of grey water recycling would have to tie in with a switch to biodegradable soap products and a general awareness of what goes down the drain. In Australia, where water shortages have spurred innovation and public education in this field, there are grey water standards for different types of irrigation, recognizing that fruit trees and forage crops represent a small contamination risk, compared to fresh vegetables like lettuce.

As with food and energy, water is still too cheap in this part of the world to inspire significant changes. But it may not be long before we start to feel the pinch. For now, be aware that there are restrictions on grey water use in many municipalities. It’s advisable to check with your local building officials and health department before proceeding with any grey water system.