Project Drawdown defines low-flow fixtures as the use of low-flow showers and taps in the household. This solution replaces the use of conventional taps and showerheads.
To determine the overall impact of water saving in the home, an analysis of low-flow taps and showerheads was undertaken to estimate the worldwide domestic water savings, energy savings, and greenhouse gas emissions reductions in high-growth scenarios of adoption of these devices. Other water saving measures in the home—such as low-flow toilets and washing machines—may also provide marginal energy savings, but these were not included to simplify the analysis. Taps and showerheads were examined because they are relatively cheap to implement, pose minimal challenges when retrofitting, and can significantly reduce water and energy consumption.
Total Addressable Market
This estimate takes into account a growing world population, increasing wealth, and national wealth distributions. The total addressable market (TAM) is the total amount of residential water demanded globally for populations with a gross domestic product per capita of at least 10,000 international dollars, and amounts to 69 trillion liters in 2018. Populations with lower wealth generally use much less water: in some cases they have no pipe-borne water to their homes, and for 20 percent of the world’s population water is not even available at community standpipes. Therefore, water-saving devices, which assume pipe-borne water, are not considered for these populations in this analysis.
For the target market, however, 59 percent of existing faucets and showerheads were taken as low-flow devices in 2018: that is the current adoption. This is based on a survey of 10,000 residents in 10 countries of the Organization for Economic Cooperation and Development (OECD). We consider that this value may be an overestimate for the entire TAM, which includes non-OECD countries. However, we also consider that this value, referring to 2007, must be an underestimate for the countries in question for 2018.
The main drivers of adoption of low-flow taps and showerheads were assumed to be population and wealth, as indicated earlier. Adoption of these devices can increase in two ways: replacement of high-flow devices for the remaining percent of the market (retrofitting), and increasing the number of people above the minimum wealth threshold (rising wealth).
Impacts of increased adoption of low-flow fixtures from 2020 to 2050 were generated based on two growth scenarios. These were assessed in comparison with a Reference Scenario, in which the solution’s market share was fixed at the current levels.
- Scenario 1: In this scenario, a 3 percent retrofit rate is assumed on existing fixtures of the TAM (assumed to equate to the existing Reference water demand) and 65 percent of all new Reference demand is assumed to use the solution
- Scenario 2: In this scenario, a 5 percent retrofit rate is assumed on existing fixtures of the TAM (assumed to equate to the existing Reference water demand) and 80 percent of all new Reference demand is assumed to use the solution
In both scenarios, the water demand drops as a result of the solution adoption which saves 15.8 percent of water on average.
Grid emissions were captured for water heating was done by electric heaters, and that less water used meant less water heated. Fuel consumed for water heating was also estimated and heated water saved translated to fuel saved. For these, emissions factors guided by the Intergovernmental Panel on Climate Change (IPCC) were used.
Purchase costs for adoption of low-flow fixtures as well as conventional fixtures were estimated using 38 total data points, and combined with 6 data points on professional installation costs to estimate the total first costs at US$25 per low-flow fixture. Operating cost differences were averaged from 10 data points and were assigned to the conventional fixtures, with operating costs for the solution kept at 0. This represented the cost difference only, and included the cost of the water saved.
The results of Scenario 1 suggest that the greenhouse gas abatement potential is 0.91 gigatons of carbon dioxide-equivalent gases from 2020 to 2050. In the Scenario 1—with 81 percent adoption of low-flow taps and showerheads—even with a net cost of US$1.5 billion, the lifetime operating savings are roughly US$477.9 billion due to water heating cost savings. The figures for Scenario 2 show 1.56 gigatons of carbon dioxide equivalent avoided along with US$765 billion in lifetime operating costs for only US$2.4 billion in net costs.
Given that there could be a tremendous increase in domestic water demand over the coming 30 years (demand is forecast to increase by 270 percent), the implementation of the low-flow fixtures solution appears very reasonable, especially as the cost of retrofitting existing taps/showers is not great. A co‐benefit of domestic water saving is a reduced reliance on overstretched freshwater supplies, reduced energy consumption, and reduced need for new water and energy infrastructure. Water and energy supply are two essential services that cross over in what is called the “water-energy nexus.”