Grey Water VS Black Water

Grey Water VS Black Water : Why It is Important to Know

Last Updated on May 22, 2023

Water is an essential resource, and we cannot live without it. It is vital for many household activities, from cooking to cleaning to flushing the toilet.

However, what exactly is this water? How safe is it to use? Does it contain harmful bacteria or harmful chemicals? And how do we know when it’s safe?

When water is used, it becomes wastewater. A large amount of wastewater is generated due to daily life activities such as bathing, toilet flushing, laundry, dishwashing, etc.

Furthermore, there are two types of wastewater: Greywater (also known as sewage or brown water) and black water. The main difference between grey water vs black water is the level of contamination.

Gray water and black water are difficult to distinguish in many situations. As an RVer, it is essential to understand the differences because they have different features. Let’s discuss both of them.

What is Grey Water?

What is Grey Water

Gray water is wastewater that comes from water in the home, excluding toilet wastewater. It includes water from showers, baths, washing machines, and washing dishes.

The water from these sources is generally considered safe for watering plants and flushing toilets. Greywater containing food particles can nourish plants.

But it may still contain some contaminants, but not enough to pose a human health hazard. You can find some most common wastewater treatment options for greywater.

What is Black Water?

Blackwater is wastewater from toilets and kitchen sinks, including anything that enters the drain of a bathroom or an approved sewerage facility.

It can include water from the bathroom, shower, toilet bowl, and washing machines after clothes have been washed. This water can also carry disease-causing bacteria that can be harmful to humans.

The water we flush down our RV toilets is highly contaminated with urine and feces and should never be used for any purpose other than flushing a toilet. You may find little or no treatment available in your area.

It also includes non-toilet water sources that any of the following has contaminated:

  • Food particles
  • Human waste
  • Human body fluids
  • Any other potentially infectious materials
  • Any substance that can endanger public health

Grey Water VS Black Water: The Difference

The Difference Between Grey and Black Water

Although both grey water and black water are wastewater, the major difference between the two is their level of contamination. Moreover, there are many criteria to differ these two types of contaminated water, such as:

01. Color: The black water is usually dark and murky, and greywater is light in color.

02. Smell: The black water has a bad smell, whereas the greywater smells like clean laundry or dish soap.

03. Contents: The black water contains human waste and toilet paper, which the gray water does not have.

04. Disinfection: The black water requires immediate disinfection, whereas gray water does not.

05. Salt Content: The black water has high salt content, and the greywater has a low salt content.

06. Solid Contamination: Solid materials such as disposable wipes or cotton pads do not break down in the sewer system, whereas solid materials in the greywater will break down.

07. Temperature: The temperature of black water is higher than that of gray water.

08. pH Level: Blackwater has a low pH level, whereas greywater has high pH levels.

09. Biological Oxygen Demand (BOD): The BOD is much less in greywater than black water.

10. Chemical Oxygen Demand (COD): The COD is much less in greywater than black water.

11. Nitrogen Content: Nitrogen content is much more in black water than greywater.

12. Biological Activity: Blackwater has higher biological activity than greywater.

Greywater or Black Water – Which is Better for the Environment?

The Environmental Impact of Greywater and Black Water

Greywater is better for the environment because it contains fewer pollutants. It has fewer harmful household chemicals, fewer solids, and lower amounts of nitrogen.

It does not include human waste, making it easier to clean and sterilize. Moreover, gray water tanks do not contain toilet paper, eliminating contact with fecal matter.

Blackwater contains higher levels of all the contaminants, as mentioned earlier. The black water will never be used for anything other than washing and flushing toilets because of its high levels of pollutants.

There are several accredited treatment systems available for the treatment of black water outdoors. By far, the most common wastewater treatment and reuse system is an aerated system.

Furthermore, it also includes water from bathroom sinks which means that you are flushing contaminated waste down your drain pipe and into your black water tank or sewer system.

Greywater and Black Water Management for RVers

When it comes to wastewater management for RVers, the decision becomes a lot more complex since both have their pros and cons.

Here’s how you can determine which option to go with:

1.     How Long You Have Been Staying on Campsite

If you stay in an area for less than five days, greywater may be the best option, but blackwater will probably be the better option if you stay longer than seven days.

2.     Where your RV is Located

Blackwater is preferable when you are in a campground because it reduces exposure to pollutants and decreases sewer hookup requirements. However, if you are boondocking or dry camping, greywater may be the best option.

3.     How Often You are Dumping

How Often You Are Dumping

If you are dumping your black water tank frequently, blackwater will be the best option because of its shorter processing time.

However, if you stay longer or have problems with gray tank odor or capacity, greywater may help solve this problem.

  • Availability of Dumping Stations

If there are more available dumping stations near your camping area, it is easier to dump black water more frequently than dump gray water, which requires more time and effort.

  • Your Dumping Methods

If your dumping method is not sterile, greywater may be the best option since it has fewer contaminants compared to black water.

  • Your Freshwater Tank Capacity

It is easier to stay in the greywater area if you have a bigger freshwater tank capacity since less water will need to be collected and dumped.

  • Your Wastewater Capacity

Staying in the black water area for longer is easier if you have a bigger black water tank capacity since more wastewater can be collected at once and dumped quickly on-site.

  • Frequency of Dumping

Staying in an area with greywater requires less frequent dumping than staying somewhere with blackwater, which means it will be easier to dump greywater promptly.

  • Distance of Travel

It is easier for RVers traveling short distances to carry the wastewater containers if they are using greywater.

However, it is essential to note that not all municipalities allow recreational vehicles or RVs with “septic tanks” to cross their borders.

  1. Convenience

Staying water in an area with greywater is more convenient since it takes less time and effort to collect and dump wastewater than blackwater, which requires dumping at a certified station.


Let’s talk about some common questions that people have:

01. Is Sewage or Brown Water Turn Black Overtime?

Is Sewage or Brown Water Turn Black Overtime

It depends on the number of solids that are in your wastewater tank. If you have a larger quantity of solids, they will decrease the water’s color.

02. Does Grey Water Become Black Water?

Yes, but that depends on the level of pollutants in your greywater tank since higher levels will decrease the water’s color. But it is essential to keep in mind that greywater can transform into blackwater within 48 hours.

03. Are There Any Biological or Chemical Treatment Systems for Grey Water?

Yes, there are several biological treatment systems and chemical treatment systems available for greywater. It is also important to note that bleach or chlorine will not make your wastewater safe or sanitary.

04. Can Urine Go in a Gray Water Tank?

Dumping the urine in a greywater holding tank is not recommended as it can clog the drain field and cause odor problems. Your gray water tank will eventually begin to smell extremely foul as urine builds up even more disease-carrying bacteria.

In Conclusion

If you’re looking for a way to conserve water and reduce your impact on the environment, greywater may be an option. By reading our article about grey water vs black water, you may better understand greywater and blackwater.

However, it should not contact food crops because of potential contamination concerns.

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