Does Saving Water Save CO2?
We know that saving water can help the environment in a myriad of ways; but did you know that saving water also helps reduce greenhouse gas emissions?
In previous blog posts, we have discussed how saving water can help lower your water bill.
But did you know how much CO2 goes into bringing one litre of water into your building?
Let’s take a look.
Treating & Pumping Water
Bringing water into a building begins at the municipal level, where water must first be treated and pumped. This previous blog post illustrates the cycle of water.
How much energy does this process take?
In Canada, the Ontario Government reported 38% of municipal electricity is consumed on pumping & treating water.
According to Gridwatch, 60% of Ontario’s power generated is nuclear and another 1.3% is wind, both of which are carbon neutral. This leaves 38.7% of energy sources generating carbon (29.1% of this is hydro, which uses carbon in its early years and then has a lower carbon footprint in later years, so we will leave it in the calculation). This means 22% of Ontario’s municipal energy that’s used to pump & treat water uses CO2.
According to the guide for York Region in Ontario, the average water use per capita in Canada is 251 litres per person. Ontario’s current population is 14.57 million people, so Ontario uses 365,707,000 litres of water per day.
End-use demand in Ontario in 2017 was 3 035 petajoules (PJ) for the year.
22% of 3,035 pJ is 667 pJ, which means 1.82 pJ/day are used in Ontario to pump and treat water.
Since 365,707,000 litres of water are used in Ontario per day, this means 1,820,000,000 mj/365,707,000 = 4.97 mJ/L is used to pump & treat water. This equates to 1.38 kW/h or 0.003 metric tons of CO2.
In the USA
In the US, more than 13% of the nation’s electricity consumption, or nearly 521 billion kilowatt hours (kWh), is associated with water-related energy use.
Energy used to move, treat, distribute, and use water produces nearly 290 million metric tons of carbon dioxide annually – the equivalent of 5% of the US’s overall emissions.
More than 8.5 billion gallons of drinking water are produced annually by the utilities that submitted data. The total energy used to produce this volume of water is just over 22 million kilowatt hours.
Now let’s look at energy to heat water, using our previous guide that the average water use per capita in Canada is 251 litres per person.
Using the hot water table and York Region guides above, we can extrapolate that:
Toilets use 65L-100L (we will round to 88L) of water per day, and no hot water.
Showers use anywhere from 28.5L-300L (we will round to 100L) water per day, and 73.1% (73.1L) of that is hot water.
Faucets account for 15% of household water use, or 37.65L. 72.7% of that is hot water, or 27.37L.
Dishwashers account for 10% of household water use, or 25.1L. 100%, or 25.1L, of that is hot water.
This means that…
Total household water usage: 251L
Total hot water usage: 125.57L
Using this calculator, heating 125.57L from 20C to 38C uses 2.61 kW/h. Which is equal to 0.00001 metric tons of CO2 for 100L.
This value can vary depending on the temperature the water is heated to, and the temperature that the water starts at (especially in the winter, when the water must be heated from cooler temperatures).
0.00001 metric tons of CO2 to heat 1L + 0.003 metric tons of CO2 to pump & treat 1L = 0.00301 metric tons of CO2 to heat, treat, and pump 1L of water.
For each L of water, this is equal to
7.6 miles driven by a passenger vehicle
0.337 gallons of gasoline consumed
3.3 pounds of coal burned
366 smartphones charged
In the US
In Michigan, 17% of all residential energy use goes to heating water.
Nationally, 70% of residential water is heated with natural gas and 29% is heated with electricity.
The total energy used for water treatment, residential use, and wastewater treatment contributes more than 83,219 lbs CO2/MG of water. Associated with the more than 8.5 billion gallons of water treated and used, plus 22 billion gallons of wastewater treated in the watershed each year, 178 million lbs or nearly 89,000 tons of carbon dioxide are emitted.
Now that we’ve looked at the numbers for the impact of saving even 1 litre of water, consider how great the impact would be in a multi-unit residential building saving hundreds of litres of water each day.