HEALTH AND SANITATION 35
smooth piping ) but the real world has shown more and more backups in sewer systems as a result of lower and lower flow rates going into sanitary systems ;
• “ The effect that toilet fixture designs have on drain line transport in long building drains has been found to be minimal . Instead , flush volume , toilet paper , and pipe slope were found to have a large effect upon drain line transport of solid waste ;” and
• Smaller pipe size was shown to have “ no significant impact on drain line carry .”
So what does this all mean ? That we have potentially hit a wall in water conservation . In theory , if we reduce sewer pipe sizes , we should be able to decrease toilet and other plumbing fixture flow rates continuously . However , in practice , we are operating on a bell curve in which as we decrease flow rates , physics seems to tell us that smaller pipe sizes make no difference . We may not be able to go any lower in our flow rates without negatively impacting public health and safety .
The front end – domestic water While sanitary systems engineering may be hitting the wall of physics , domestic water is another story . David LaFrance , CEO of the American Water Works Association , once said , “ People think that water is simple , but it is highly complex .” Domestic water – because of the complexity of distribution systems ’ layout , water quality and performance needs , among other requirements — means there is more opportunity in right-sizing water systems .
The problem has mostly been that these complexities were not even accounted for when water usage rates were reduced .
A similar method was created in the 1940s to size domestic water systems . This method had remained largely unchanged for the past 80 years . In essence , it treated every building in the U . S . as if it were a sports stadium at halftime — assuming long queuing lines for the restrooms and numerous plumbing fixtures being ‘ on ’ simultaneously . At the time , this methodology was groundbreaking .
However , in the past 80 years , as water conservation concerns have increased , no updates were made to this process . The volume of water stored in the pipe remained the same while the flow rates were reduced . This increased the duration of time water was in piping , which led to numerous negative side effects . Water age increased as flows decreased , leading to such negative second-order effects , such as :
• Hot water delivery times increased ( decrease in energy inefficiency );
• Disinfectants in the water decreased while disinfectant byproducts increased ( decrease in safety );
• Waterborne pathogens such as Legionella pneumophila increased ( decrease in safety ); and
• Corrosion of water piping systems increased ( decrease in reliability ).
It has gotten to the point that even the National Academy of Sciences , Engineering and Medicine ( NASEM ) has weighed in . In its 2019 consensus report on the management of Legionella in buildings NASEM stated :
“ Low-flow fixtures should not be allowed in hospitals and long-term care facilities because of these buildings ’ high-risk occupant populations . Low-flow fixtures have been promoted to conserve water and , in some cases , energy . Because of their low flow , however , these fixtures , primarily low-flow faucets but also showers , increase water age , and restrict disinfectant levels , including the disinfection provided by elevated water temperatures . As such , low-flow fixtures present a greater risk for Legionella development in the plumbing systems that feed them .”
To have NASEM come out with this kind of statement should catch your eye . For a governmental body to implicate that water conservation is at odds with water safety is no small matter . This shows the complexity and need for research and investment in plumbing system design and construction , particularly in pipe sizing . Fortunately , this research is happening . PA
© Plumbing Africa Rory Macnamara
It is what is behind the outlet that counts !
“,,,, as water conservation concerns have increased , no updates were made to this process .”
April 2023 Volume 29 I Number 2 www . plumbingafrica . co . za