• CASE Report by TRC Companies and Frontier Energy for the California Energy Commission Detailing Energy and Water Savings by the Water Demand Calculator
• Lawrence Berkley National Laboratory Studies that Discuss Structural (i.e. Right Sizing) and Behavioral Water Saving
  • Water and Energy Wasted During Residential Shower Events: Findings from a Pilot Field Study of Hot Water Distribution Systems
  • Reducing Waste in Residential Hot Water Systems
• Reach Codes Path (California Energy Codes and Standards, below reports on this webpage as well)
  • UPC Appendix M Report (has safety factor tables for peak flow rate)
  • UPC Appendix Report (executive summary)
  • UPC Appendix M Fact Sheet
• Study that sought to understand peak and off-peak water demand patterns for the purpose of more accurately and economically sizing water service lines and water meters: Assessing Water Demand Patterns to Improve Sizing of Water Meters and Service Lines | The Water Research Foundation
• California Adoption of Water Demand Calculator site with training links
• EPA WaterSense study showing that water efficiency leads to energy savings
• The California Energy Code is considering to require the use of the Water Demand Calculator for multifamily construction as part of the prescriptive approach.  In Title 24 document 255321-4 | 2025 CASE Report Multifamily Domestic Hot Water the author determined water and energy savings from utilization of Appendix M was about 260 Gallons per year per dwelling unit and 1.4 kWh per year per dwelling unit, equaling over 9 million gallons of water saved and 50,000 kWh in energy reduced:

Executive Summary:

The California Energy Code prescriptive approach:

Additional Information:

The documents worth referencing via are:

• 255321-4 | 2025 CASE Report Multifamily Domestic Hot Water 
• 255324-3 | Staff Supplement to 2025 CASE Report - Multifamily Domestic Hot Water

Particularly the 2025 CASE Report is filled with information continually mathematically modeling the energy and water savings.  Some highlights below:

The water and energy conservation advantages of smaller-diameter distribution networks have been demonstrated and described in many peer-reviewed publications published beginning in the 2000s and perhaps before. The reported benefits and studies supporting them are as follows (full list can be found at the bottom of the article): 

• Smaller-diameter pipes produce water savings through reduced waiting times for hot water (less water is wasted to drain waiting for hot water arrival) (Ferreira and Goncalves, 2020; Lutz, 2011; Omaghomi and Buchberger, 2018) 
• Smaller diameter pipes have lower distribution system energy losses (particularly losses associated with cooldown of heated water between hot water draws) than larger diameter pipes and fittings (Chen et al., 2021; Healy et al., 2021; Hendron et al., 2009; Hiller, 2011, 2006, 2005a, 2005b; Josey et al., 2023; Josey and Gong, 2023; Lutz, 2011, 2005; Omaghomi and Buchberger, 2018; Parker et al., 2015). Studies universally identify hot water distribution energy losses as the primary source of wasted energy and as the best opportunity for mitigating energy losses. 
• Smaller diameter service lines and meters produce more accurate metering, better cost recovery by utilities and enhanced ability to detect leaks for building owner/operators (Creaco et al., 2016; Douglas et al., 2019). 
• Smaller diameter pipes result in more frequent and complete turn-over of water in distribution systems, with potential water quality benefits (Bédard et al., 2018; Clements et al., 2023; Josey and Gong, 2023; Lautenschlager et al., 2010; Nisar et al., 2020; Rhoads et al., 2022; Schück et al., 2023; Ye et al., 2022). This is particularly important for systems with low-flow fixtures, but mismatched distribution systems not sized for flows of the low-flow fixtures. This potential benefit remains a topic of study, since water quality studies of green buildings have generally shown worse chemical and biological water quality than in comparable conventional systems. Researchers have hypothesized that worse water quality in green buildings can be attributed to higher surface-area-to-volume ratio for smaller diameter pipes and to reduced water usage (less turnover). Alternatively, degraded water quality in green buildings could be the result of system designs and operation that are inconsistent with low-flow fixtures and modern water usage and might be mitigated via smaller diameter (right-sized) distribution systems and periodic purging.
• Smaller-diameter networks have lower materials costs than larger diameter networks (Ferreira and Goncalves, 2020; Josey and Gong, 2023). 

Peer Reviewed Studies highlighting the benefits of right sizing including water savings, energy savings, and improved water quality.

1. Bédard, E., Laferrière, C., Déziel, E., Prévost, M., 2018. Impact of stagnation and sampling volume on water microbial quality monitoring in large buildings. PLoS One 13, e0199429.
2. Chen, Y., Fuchs, H., Schein, J., Franco, V., Stratton, H., Burke, T., Dunham, C., 2021. Water heating energy use reductions from EPA WaterSense lavatory plumbing fittings. Resources, Conservation and Recycling 174, 105781. 
3. Clements, E., Irwin, C., Taflanidis, A., Bibby, K., Nerenberg, R., 2023. Impact of fixture purging on water age and excess water usage, considering stochastic water demands. Water Research 245, 120643. 
4. Creaco, E., Kossieris, P., Vamvakeridou-Lyroudia, L., Makropoulos, C., Kapelan, Z., Savic, D., 2016. Parameterizing residential water demand pulse models through smart meter readings. Environmental modelling & software 80, 33–40. 
5. Douglas, C., Buchberger, S., Mayer, P., 2019. Systematic oversizing of service lines and water meters. AWWA Water Science 1, e1165. https://doi.org/10.1002/aws2.1165 
6. Ferreira, T.D.V., Goncalves, O.M., 2020. Stochastic simulation model of water demand in residential buildings. Building Services Engineering Research and Technology 41, 544–560. https://doi.org/10.1177/0143624419896248 
7. Healy, W.M., Hiller, C., Lutz, J., 2021. How Residential Water Heating is Changing. ASHRAE Journal 63, 62–66. 
8. Hendron, R., Burch, J., Hoeschele, M., Rainer, L., 2009. Potential for energy savings through residential hot water distribution system improvements, in: Energy Sustainability. pp. 341–350. 
9. Hiller, C.C., 2011. Hot-water distribution system piping heat loss factors–phase III: test results. ASHRAE Transactions 117, 727–742. 
10. Hiller, C.C., 2006. Hot Water Distribution System Piping Heat Loss Factors–Phase I: Test Results. ASHRAE transactions 112. 
11. Hiller, C.C., 2005a. Comparing Water Heater vs. Hot Water Distribution System Energy Losses. ASHRAE transactions 111. 
12. Hiller, C.C., 2005b. Rethinking school potable water heating systems. ASHRAE Journal 47, 48. 
13. Hobbs, I., Anda, M., Bahri, P.A., 2019. Estimating peak water demand: Literature review of current standing and research challenges. Results in Engineering 4, 100055. 
14. Josey, B.M., Buchberger, S.G., Gong, J., 2023. Comparing Actual and Designed Water Demand in Australian Multilevel Residential Buildings. J. Water Resour. Plann. Manage. 149, 05022013. https://doi.org/10.1061/(ASCE)WR.1943-5452.0001625 
15. Josey, B.M., Gong, J., 2023. Determination of Fixture-Use Probability for Peak Water Demand Design Using High-Level Water End-Use Statistics and Stochastic Simulation. J. Water Resour. Plann. Manage. 149, 05023015. https://doi.org/10.1061/JWRMD5.WRENG-6146 
16. Lautenschlager, K., Boon, N., Wang, Y., Egli, T., Hammes, F., 2010. Overnight stagnation of drinking water in household taps induces microbial growth and changes in community composition. Water research 44, 4868–4877. 
17. Lutz, J., 2011. Water and energy wasted during residential shower events: Findings from a pilot field study of hot water distribution systems. 
18. Lutz, J., 2005. Estimating Energy and Water Losses in Residential Hot Water Distribution Systems. Lawrence Berkeley National Lab.(LBNL), Berkeley, CA (United States). 
19. Nisar, M.A., Ross, K.E., Brown, M.H., Bentham, R., Whiley, H., 2020. Water stagnation and flow obstruction reduces the quality of potable water and increases the risk of legionelloses. Frontiers in Environmental Science 8, 611611. 
20. Omaghomi, T., Buchberger, S.G., 2018. Residential Water and Energy Savings in Right-Sized Premise Plumbing:(045), in: WDSA/CCWI Joint Conference Proceedings. 
21. Parker, D.S., Fairey, P.W., Lutz, J.D., 2015. Estimating daily domestic hot-water use in North American homes. ASHRAE Trans 121, 258–270. 
22. Rhoads, W.J., Sindelar, M., Margot, C., Graf, N., Hammes, F., 2022. Variable Legionella response to building occupancy patterns and precautionary flushing. Microorganisms 10, 555. 
23. Schück, S., Díaz, S., Lansey, K., 2023. Reducing Water Age in Residential Premise Plumbing Systems. J. Water Resour. Plann. Manage. 149, 04023031. https://doi.org/10.1061/JWRMD5.WRENG-5943
24. Ye, C., Xian, X., Bao, R., Zhang, Y., Feng, M., Lin, W., Yu, X., 2022. Recovery of microbiological quality of long-term stagnant tap water in university buildings during the COVID-19 pandemic. Science of The Total Environment 806, 150616.