How big does a food truck grey water tank need to be?
Short answer
Most US health departments require the grey (waste) water tank to be at least 15% larger than the fresh water tank, so a 30 gal fresh tank needs a grey tank of 35 gal or more. Some counties ask for 25% or even 50% larger, so confirm the figure with the health department where you will operate before your builder orders tanks.
Last reviewed by the Trailer3D editorial team. Uses the same equipment data and checks as our 3D studio.
Not sure? Handwashing only (pre-packaged food) can need as little as 5 gal; a full cook line with a 3-compartment sink usually carries 30 to 50 gal.
Why the waste tank is bigger
Everything you pour out of the fresh tank ends up in the grey tank, plus melted ice, liquids from food and the water you use to clean. A bigger waste tank means you never have to stop service because the waste is full, and never dump grey water on the ground, which is illegal everywhere.
How much fresh water to carry
It depends on your menu. A unit that only serves pre-packaged food may need just enough for handwashing; a full cook line with a 3-compartment sink usually carries 30 to 50 gallons. Your health department will often set a minimum for your menu type during plan review.
Water is heavy: 8.34 lb per gallon. A full 50 gal fresh tank adds over 400 lb, which matters for trailer axles and truck payload.
Worked examples
| Fresh tank | Grey at +15% | Grey at +25% | Grey at +50% | Fresh water weight |
|---|---|---|---|---|
| 10 gal | 12 gal | 13 gal | 15 gal | 83 lb |
| 20 gal | 23 gal | 25 gal | 30 gal | 167 lb |
| 30 gal | 35 gal | 38 gal | 45 gal | 250 lb |
| 40 gal | 46 gal | 50 gal | 60 gal | 334 lb |
| 50 gal | 58 gal | 63 gal | 75 gal | 417 lb |
| 60 gal | 69 gal | 75 gal | 90 gal | 500 lb |
Menus use the equipment our studio places for that menu (see menu benchmarks). Estimates for planning, not engineering approval: your builder, health department and fire marshal have the final word.
Questions
Does the water heater count toward fresh water?
Usually not. Most departments size the waste tank from the fresh water tank capacity; ask yours if you carry a large water heater.
Where do I empty the grey tank?
At your commissary or another approved dump point. Your plan review normally asks where you will dispose of waste water.
Can I use a portable tank instead?
Some departments allow portable fresh and waste containers for small carts; most require permanently mounted tanks for trucks and trailers.
Sources and assumptions
- 15% larger waste tank: common US health-department mobile food unit requirement (for example Indiana county mobile food packets); some jurisdictions require 25% or 50%
- Water weight: 8.34 lb per US gallon