Quantification of Exposure-Related Water Uses for Various U.S. Subpopulations


Executive Summary

A realistic assessment of exposure and risk to water-borne contaminants requires accurate summaries of water usage patterns. This report examines population water-use behavior for showers, baths, clothes washers, dishwashers, toilets and faucets derived from a review of current literature as well as analyses of the National Human Activity Pattern Survey (NHAPS), the Residential End Uses of Water Study (REUWS), and the Residential Energy Consumption Survey (RECS), and ingestion behavior derived from analyses of the Continuing Survey of Food Intake by Individuals (CSFII).  The NHAPS database was compiled as a result of an EPA supported survey, conducted between October 1992 and September 1994, with the goal of collecting a rich set of exposure-related behavioral data.  Detailed analysis of NHAPS has been completed for some exposure assessment purposes (Tsang and Klepeis, 1996), but the water-use behavior with respect to exposure to water-borne contaminants has not been thoroughly analyzed.  The REUWS database was compiled through an American Water Works Association Research Foundation project (AWWARF Project# 241) conducted between May 1996 and March 1998 with the goal of understanding how water is used and to identify potential for water conservation (Mayer et al., 1998).  As such, this database also has not been analyzed for water-use behavior with respect to exposure to water-borne contaminants.  In this paper, NHAPS and REUWS (and to a lesser extent, RECS) are extensively analyzed as a function of a variety of demographic characteristics for the purpose of using this behavioral information in assessing exposure.  CSFII is analyzed to quantify ingestion of drinking water as a function of demographic characteristics.


Linking the use of contaminated water with exposure and potential risk can be accomplished using an exposure model that represents the factors leading to the release of, and contact with, the contaminant.  Such a model must represent the physical environment, the emission characteristics of the water appliances during their use, and the water-use and location behavior of the occupants. Subsequently, the model must account for the principal routes of exposure: inhalation, dermal contact, and ingestion. The water-use characteristics and distributions discussed and presented in this report are analyzed such that the data can effectively be utilized by an exposure model (such as the Total Exposure Model (TEM)) when simulating realistic occupant water-use behaviors of various populations.


NHAPS contains responses to questionnaires and 24-hour time-location-activity diaries from over nine thousand U.S. residents who recalled the frequencies and durations of the previous day’s activities. NHAPS is analyzed in this report to quantify characteristics of various household water uses, including the use of showers, baths, clothes washers, dishwashers, faucets, and drinking water intake.  REUWS holds water-use data (duration, volume and flowrates of water-use events) for 1,188 households acquired using a magnetic data logger attached to the household water supply pipe. The REUWS data is analyzed in this report to quantify frequency, duration, volume and flowrate characteristics for various water uses, including the use of showers, toilets, faucets, and clothes washers. RECS contains energy related water-usage information obtained from questionnaires from 5,900 residential housing units. The RECS database is analyzed in this report to quantify estimates on household clothes washer and dishwasher usage. CSFII contains tap water consumption data collected through dietary recall interviews with approximately 15,300 people. The CSFII data are analyzed in this report to quantify estimates of per capita water ingestion for both direct water (plain water consumed as a beverage) and indirect water (water used to prepare foods and beverages).


When applicable, the frequencies and duration data from NHAPS, REUWS and RECS, segregated by demographic characteristics (such as gender, age, education, employment status, U.S. EPA region, etc.), are analyzed and compared for each type of water use. After comparing the databases, it is concluded that databases based on recall surveys, like NHAPS and RECS, are reliable sources for frequency information of occasional events such as showers, baths, and dishwasher and clothes-washer use, but are unreliable in reflecting more frequent events such as faucet use. In regard to all frequency questions asked in the surveys, it is very clear that the way the questions were asked had a large impact on the quality of the data. REUWS, which is based on analysis of waterflow signatures through household water meters, is an excellent source for water-use duration information. Overall, NHAPS data are more reliable than REUWS for frequency information, while REUWS data are more reliable than NHAPS for duration information. The reasons for this lie within the manner in which the databases were compiled. NHAPS was compiled from a recall telephone survey of the respondents’ activities of the previous 24 hours. Respondents were able to remember how many showers and baths they took, while they had difficulty estimating the durations of the events, as the duration values appeared to be overestimated and clustered around 5 minute intervals. In contrast, REUWS was compiled from direct mechanical measurements of water usage logged at household water meters and subsequent waterflow disaggregation by a software program, Trace Wizard, to determine individual water uses. REUWS contains measured values of duration, volume, and flowrates of the water-use events in its database. For this reason, REUWS provides very accurate duration data. However, REUWS has a few integral limitations that make it less reliable in reference to frequency data, such as the inability to discern which person is performing the water uses in question, and at times Trace Wizard mislabeled events as they were clearly unrealistic. In regard to the frequency of clothes-washer and dishwasher use, the RECS database was the most reliable source as the survey questions were more straightforward than those asked for NHAPS. Dishwasher and clothes-washer durations and volumes are best characterized using a combination of data from REUWS, data provided by the manufacturers, and data from field experiments. Only REUWS provides usable information on faucet and toilet use.





Last modified on November 2006.