Martin's toilet rain water harvesting spreadsheet
Find out how much water and money you flush down the toilet every year!
Put your household details in the white cells of the second column in the spreadsheet below. You can find typical values from the tables underneath the spreadsheet or the hyperlinks within the spreadsheet.
The default values in the spreadsheet are for a 2 bedroomed house in Anglesey, North Wales.
Apologies, I havent found a way of keeping the calculated costs to 2 decimal places.
This sheet was built using Trimpath and Javascript
| Put your household details here | |
| Annual average rainfall (mm) | 850 |
| Roof area (m2) | 30 |
| Fraction of rainfall collected by your roof (0 -1) | 0.8 |
| Toilet flush volume (litres) | 6 |
| Toilet flushes a day | 10 |
| Price paid for water and sewerage (£) | 2.53 |
| . | . |
| Results | . |
| The most water on average that can be collected ('000 litres per year) | |
| Tank storage needed ('000 litres) | |
| . | |
| Water flushed per day (litres) | |
| Volume of water flushed ('000 litres per year) | |
| . | . |
| Cost of water flushed a year (£) | |
| The most that could be saved a year using rain water harvesting from your roof (£) |
| Roof type | Roof area range (m2) |
| Shed | 2 to 20 |
| 2 bed house | 20 to 35 |
| 3 bed house | 30 to 45 |
| 5 bed house | 45 to 70 |
| Chapel | 60 to 150 |
| Roof collection coefficient | |||
| Material | Steep (>45%) | Shallow (45-20%) | Flat (<20%) |
| Slate, tile, metal sheet | 0.98 | 0.8 | 0.6 |
| Shingles | 0.7 | 0.6 | - |
| Felt and Gravel | - | 0.4 | 0.2 |
| Bare ground | 0.5 | 0.2 | 0.05 |
| Toilets | |
| Toilet flush volume (litres) | Flush type |
<6 |
Very low flush |
6 |
Standard low flush |
9 |
Pre 2000 standard flush |
>9 |
old fashioned toilet cistern |