Water & carbon saved by sharing a bath
Baths can use anything from 80 to over 200 litres of water, so around twice the volume of water of a shower.
Sharing the bath water helps to make the most of it, and saves energy and CO2. We have taken a midway average figure for a filled bath of 150 litres, and so saving 150 litres of water based on 2 sharing.
Carbon saved by sharing a bath
Amount of CO2 emitted by boiler to heat bath water:
Assume a standing cold water temperature of 10°C
Assume boiler temperature is set to 60°C
Assume 80% of bath water is hot, mixed with 20% cold, so 80% of 150 litres is 120 litres.
Carbon footprint of unheated tap water is relatively small, around 0.0003 kg per litre so = 0.0003 x 30 litres = 0.009 kg CO2 for cold water
For remaining 120 litres (for a thermostat temperature of 60°C):
Energy needed to heat 1 litre by 1°C = 0.0011kWh
Carbon intensity of gas = 0.19 kg CO2 per kWh
Temperature elevation needed from 10°C to 60°C = 50°C
Energy needed to heat water to 60°C = 0.0011 kWh x 120 litres x 50°C = 6.6 kWh
So for bath of 150 litres (hot + cold) = (6.6 x 0.19) + 0.009 = 1.26 kg CO2 per bath
Using grey water
Used water, known as grey water, can be re-used for outdoor use or in the garden (although not on food crops). Here are products that will help:
Grey water Refresh
This product helps to treat your grey water, controlling the soap content and keeping it free of odours and algae. See http://www.evengreener.com/Shop/-_Seasonal_Savings_-/REFGW500_Refresh_for_Grey_Water.html
WaterGreen Hosepipe
The hosepipe allows you to easily syphon off your bath water and pumps it directly to your garden, or wherever you wish to use it.
See http://www.evengreener.com/Shop/-_Seasonal_Savings_-/DRGHTBUS_WaterGreen.html
For more tips and advice see:
Renewable Energy UK
http://www.reuk.co.uk/Greywater.htm
Selfsufficient 'ish'.com
http://www.selfsufficientish.com/greywater.htm
Dual baths & showerheads
If investing in a new bath, a dual bath like the following makes it easier for people to share.
http://www.everyfaucet.com/asp/show_detail.asp?sku=ECS1826&refid=FR76-ECS1826
Dual shower heads are also available and can be more efficient than two people or children showering separately.
http://www.trevishowers.co.uk/trevi_products/mixer_showers/trevi_ascari_dual.html
http://www.tiarashowers.com.au/products.html
Footnotes
