landplan.io - Daily Design Flow Reduction Justification
landplan.io offers a variety of ways to classify flow rate. We have residential with number of bedrooms and commercial with flow classifications.
There may be different opportunities to reduce the flow per bedroom for residential dwellings. The following is just an example how this could be justified.
Most regulations are based on 60 gallons of flow per person per day, which can be broken down by fixture to:
| Fixture | Percent | Uses/Day | Gal/Use | Gallons/Day |
|---|---|---|---|---|
| Toilet | 26.7 | 5.05 | 3.5 | 18.5 |
| Clothes Washer | 21.6 | 0.37 | 40.5 | 15 |
| Shower | 16.8 | 0.75 | 17.2 | 11.6 |
| Faucets | 15.7 | 1.4 | 8.1 | 10.9 |
| Dishwasher | 1.4 | 0.1 | 10 | 1 |
| Bath | 1.7 | 1.2 | ||
| Other | 2.3 | 1.6 | ||
| Total | 59.8 |
It is possible to argue that with the use of low flow fixtures such as toilets and high efficiency (HE) clothes washer. The use of these fixtures is a choice in most areas it is typically a more costly investment. But saving water in the front end of the house should account for a savings in the septic area required.
Here is an adjusted flow rate for the use of low flow fixtures and appliances:
| Fixture | Percent | Uses/Day | Gal/Use | Gallons/Day |
|---|---|---|---|---|
| Toilet | 15.8 | 5.05 | 1.6 gpf | 8.08 |
| Clothes Washer | 21.3 | 0.37 | 40.5 | 8.9 |
| Shower | 27.7 | 0.75 | 17.2 | 11.6 |
| Faucets | 26.1 | 1.4 | 8.1 | 10.9 |
| Dishwasher | 1.4 | 0.1 | 10 | 1 |
| Bath | 1.7 | 1.2 | ||
| Other | 2.3 | 1.6 | ||
| Total | 43.28 |
Adjusted DDF = 43.28 gallon/person/day x 2 persons/bedroom x 3 bedrooms Adjusted DDF = 259.68 gallons/day There is a shop facility on the rear of the property with a half bath (toilet and faucet) servicing a business with maximum 4 employees. Using the low flow toilet and faucet flow rates above totaling 18.98 per employee per day. An additional 75.92 gallons will be added Final Adjusted DDF = 336 gpd
For the standard computation, Standard 3 bedroom Daily Design Flow (DDF) = 360 gallons per day 360 gpd = 60 gallons/person/day x 2 persons/bedrooms x 3 bedrooms
The preceding calculations are accounting for the reduced water usage for the High Efficiency Clothes Washer (HECW) with a Water Factor of 4.0 or less and standard 1.6 gallons per flush toilet. All calculations were based on the referenced material below. The HECW with a Water Factor of 4.0 or less must be verified by the time of final inspection and needs to be worded in the permit specifications. References
- Onsite Wastewater Treatment Systems Manual. EPA 625/R-00/008. February 2002.
- http://www.epa.gov/watersense/ EPA Watersense website has lists of manufacturers of High Efficiency water appliances.
- http://www.energystar.gov/index.cfm?fuseaction=clotheswash.display_column_definitions/ Information on Water Factor label for automatic clothes washing machines.
- http://www.cuwcc.com/efficient_clothes_washers.lasso/ Information on HECWs.
- DeOreo, William. Towler, Erin. Lewis, David. Residential Indoor Water Conservation Study: Evaluation of High Efficiency Indoor Plumbing Fixture Retrofits In Single-Family Homes In the East Bay Municipal Utility District Service Area. 2003.