The quality of water that comes out of the faucets in your home may not necessarily be safe considering that water utilities are not required to monitor the quality of water that enters buildings from its supply line.

A new study, which was recently published in Building and Environment, has revealed that water quality in each room in a home can vary and can also change depending on the season. These findings challenge the common assumption that water delivered to a home from a public drinking water supply line is of the same quality as when it left the water utility, and that this remains unchanged regardless of the season.

According to Andrew Whelton, an associate professor of civil engineering and environmental and ecological engineering at Purdue University, and co-author of the paper, "this study reveals that the quality of drinking water in the service line is clearly not the same as that of the water that comes out your faucet."

For the study, which is currently the most intensive assessment of water quality throughout an individual home over time, the scientists collected 58 water samples from a single home over a one year period. While they acknowledge further studies of a similar scale are required before the findings can be generalized for other homes across the US, the results are disconcerting. They found that there was no disinfectant present in the water entering the home 10% of the time, which means that there was no protection against bacterial growth in the water once it entered the home. They also found an increase in the pH of water inside the home, together with fluctuating levels of organic carbon, both of which can suggest drastic changes in the chemistry of drinking water.

Current laws only stipulate that water utilities report on the quality of water at various points along the water distribution network. However, the quality of water monitored at these points may not necessarily represent that of water entering a building/home. And even in cases where a water utility tests for heavy metals such as copper and lead at a faucet in a building, they do not have to test the water from each faucet in the house, nor do they have to test over various seasons.

"We found that the water chemical quality varied significantly through water fixtures due to water temperature, plumbing fixture and different water uses," said Maryam Salehi, currently an assistant professor of civil engineering at the University of Memphis, and previously a postdoctoral research associate at Purdue.

Spatially within the house, they found that more than 85% of the time, the water in the water heater contained no disinfectant.

While the researchers found differences in the levels of some chemicals varied throughout the home and between seasons, most of these levels are not considered harmful according to current drinking water safety guidelines. However, while there were no children residing in the house, lead levels in water tested within the home exceeded safety levels recommended by the American Academy of Pediatrics for children. The tests also found that some lead-free plumbing fittings within the home leached lead.

According to the authors, the study's findings suggest that utility companies should perhaps be monitoring lead concentrations in homes more frequently, and that more support may be needed from government to help homeowners take the initiative to conduct water quality tests to ascertain the quality of water in their homes.

Also, several factors associated with climate change may increase the variability of water quality across seasons.

"It's known that warmer temperatures allow microorganisms to persist in source water for longer periods of time, said Jade Mitchell, an associate professor of biosystems and agricultural engineering at Michigan State University. "Heavier precipitation can also result in combined sewer overflows in some locations, while droughts affect water quantity and available source water." "After water enters a home it continues to age. Older water is more likely to have contaminants that are problematic," Whelton points out. "Because the quality of water delivered to a single home can vary significantly, and building plumbing can change the water too, predicting drinking water safety at every building faucet is currently not possible,"

According to the authors, factors such as differences in plumbing materials, the number of people living in a house, as well as other factors, all of which warrant further study, can affect the quality of water in a home. More studies such as this could help us to develop technologies that will prevent consumers from being exposed to unsafe drinking water in their homes.

"Choose plumbing designs that minimize the amount of water and time that water sits still," Whelton advises. "This should help limit microbial growth and lessen the chance that chemicals leaching from the plumbing exceed unacceptable levels. If you have an existing home, flush the faucet before taking a drink to get rid of the old water. Flushing can help bring in new, fresher water from the building entry point," he said.

It is also a good idea to filter drinking water with a good quality water purifier to remove any pathogenic bacteria that may be present, as well as other harmful contaminants such as lead.

Maryam Salehi et al. An investigation of spatial and temporal drinking water quality variation in green residential plumbing. Building and Environment (2019). DOI: 10.1016/j.buildenv.2019.106566