Balancing act needed in new buildings
Contractors strive to save H2O, but must be aware that non-potable water may be unsuitable
CAPE Town’s construction industry is being hit hard by the city’s water crisis as contractors seek alternate water sources in their daily development and building work.
Not only does this incur extra costs and logistical planning, but the Master Builders Association Western Cape warns that water from these alternate sources could pose health, safety and environment risks if the quality is not properly checked.
The industry is working hard not only to reduce its water usage, but also to construct homes that will require less water.
The Green Building Council of South Africa says the built environment currently accounts for 20% of the world’s potable water usage, and green buildings can save between 20% and 100% of the potable water a conventional building would use.
With saving this water a “major priority” in the Western Cape, Manfred Braune, executive director of certifications at the council, says green buildings are preferable as they are designed and built to save resources.
“In some cases, buildings can be designed and operated to be net positive water (generate more water than they use) and these offer benefits to the greater community.”
Both new and refurbished homes can target water efficiency.
“All buildings can be retrofitted with water-saving devices such as dual flush toilets, low-flow sanitary fittings, rainwater-harvesting tanks and grey water systems.”
When building homes, property developers and builders should also investigate Alternate Building Technologies, as some use less water during construction than traditional masonry.
They should also, wherever possible, use recycled water instead of potable water on site, he says.
Building sites must be managed to ensure water used for construction purposes is “tightly controlled”.
For some time the City of Cape Town’s water restrictions have outlawed the use of potable water for washing hard surfacing and paving, says Allen Bodill, executive director of the Master Builders Association Western Cape.
This has presented “serious challenges”, particularly topainting, decorating and paving contractors.
Bodill says it was common practice in the past to prepare existing buildings for repainting by using high-pressure washing equipment on wall and roof surfaces to remove loose and flaky materials, but this is obviously a water-intensive operation.
People have had to use alternate water sources, such as borehole and harvested rainwater and recycled effluent or natural spring water for these tasks.
“This significantly increases the cost and logistical arrangements to source, store and transport this water to site during the preparation phase of this type of work. Consideration and care also needs to be given to discharging some grades of recycled effluent water into the municipal storm water system, as there may be potential risk of contamination to the environment.”
In addition, depending on the chemical composition of the alternative water and its compatibility with the materials used in the redecorating processes, there could also be other risks.
“Some of these water sources may contain minerals and pathogens in solution which may pose both health and safety risks to the contractor’s staff, as well as presenting possible paint adhesion risks.”
As construction is broadly defined as a moderately water-in- tensive industry, Bodill says site operations such as dust suppression, cleaning of building sites, structures and contractors’ plant and equipment, as well as water supplies to temporary site ablution facilities should now all be carried out using alternative water sources.
However, structural concrete and masonry elements of the building have to be “very carefully evaluated” when considering the use of alternative water sources in their construction. This is due to the possible dangers associated with contaminants in these alternative water sources which may result in problems of durability and the structural strength of these elements.
“The professional teams overseeing the design and erection of these structures should closely monitor and approve the water quality used on site for building these elements.”
When designing and building new structures from scratch, he says the opportunity exists to install the plumbing in that will separate the potable supply fittings from a possible alternative water source, which could be used to supply toilets, garden taps, washing machines and other non-potable needs.
In addition, a common approach is to install a well-point or borehole on the site, where feasible and affordable, and then to carefully analyse and filter the water before pumping it into the domestic reticulation system.
“It is very important to establish the pH levels of this groundwate. Should this be excessively corrosive, it could result in a costly failure of components in hot water cylinders, kettles, washing machines and copper pipes and fittings.”
Installing rainwater-harvesting components as well as grey water systems on new structures, and retrofitting these to existing buildings, will all help to reduce the demand on the potable water resource, Bodill says.
“While opportunities exist to go partially or completely off the City of Cape Town’s potable water grid when constructing new buildings, or when retrofitting these to existing buildings, there are a number of risk factors which need to be considered.”
There have also been suggestions that the City of Cape Town should halt all building development until the worst of the drought crisis is over.
Responding to this recommendation, Mayor Patricia de Lillie says the city must balance very important considerations and save water while, at the same time, not compromise the economic welfare of Cape Town.
“Despite our steep population growth since 1996, our water demand has remained relatively flat due to massive conservation efforts. Our Water By-law has been a progressive piece of legislation that has been one of the key tools used to guide water demand and conservation efforts over the years.
“The city has therefore had progressive by-laws, smart-living guidelines and water-conservation programmes in place for decades. We are currently seeing how we can enhance our efforts to become a more resilient city.”
Developers embarking on construction projects, like the Elements on Main and Elements on Battery in Sea Point, are focusing on water preservation.
The Belhar Gardens social housing development was recently recognised for design excellence in greater water and energy efficiency.