Why Is Black Water Black?

When it comes to tiny houses the question is typically asked whether it is off-grid or grid-tied. Part of this discussion inevitably leads to the clean water system and waste water system. Does your tiny house have a composting toilet or a more traditional flush commode? Does your water come from some sort of holding tank either inside the house or from under it? Do you plug a garden hose into the side of the tiny house? These are all important questions and help make sense of what black water is, what grey water is, and even what potable water is.


  • Clean water is called fresh water or potable water
  • Waste water is called black water and grey water. Black is everything that gets flushed down the toilet while grey is everything that goes down the kitchen sink, the bathroom sink and your shower


Both the clean and wastewater systems on a tiny house can be problematic if not maintained properly. It is important to know the following:

If your tiny house has a water holding tank you probably think you just fill the tank up with clean water by just hooking up a garden hose. It isn’t quite that easy. We’ll call these the


  1. Always use a certified potable water hose when filling the tank or hooking to city water.  These type hoses are blue (to indicate clean water….clever!) or white or even white with a blue stripe running down it. They are colored this way so they aren’t confused for a standard outdoor hose and thereby used for a purpose that may contaminate them. Potable water hoses are made so that they don’t have a rubber odor or taste like plastic. If you choose to use a standard green or black garden hose for your potable water you won’t just have a nasty smell and taste to your water but you may also leach chemicals into your water.
  2. Water hoses must always be protected by a pressure regulator when hooked to your tiny house.  The regulator should be attached to the end of the hose that hooks to city pressure (or your water spigot). This is to protect the hose itself as well as your water pipe from high pressure that can sometimes come through your spigot line.
  3. If you do use a water holding tank, be sure to drain your water tank after every outing or every guest, in order to prevent contaminants from setting up or a bad smell occurring because of stagnant water.


If your tiny house is not directly plumbed (typically involving PVC pipe) to a septic system and instead uses a waste hose, you need to be aware of how to keep yourself, your guests, and your tiny house healthy and as sanitary as possible.

First and foremost, always use an odor tight connector or seal to hook your sewer hose to the ground sewer connection.  Now for the Greywater Tips

  1. When your tiny house is parked you may want to just dispose of grey water in an eco-friendly way (provided you use eco-friendly products like soap, dish detergent, etc) by allowing the water to drain directly through a garden hose into the grass, a garden, or around three. This is a great idea but in order to do so, you’ll need a special drain cap that downsizes your 3-inch hose to a garden hose size.
  2. When directly hooked to either a city sewer connection or a garden hose, you can leave the gray water valve open to let it drain as it’s used. There is no need to collect the grey water and then dump it when the tank is full.

Before dispensing some black water tips there is one rule that cannot be emphasized enough. Do not drain your black water tank just anywhere. You may think it is the same as composting, but it is not. Let’s proceed to some black water tips:

  1. Don’t leave the dump valve open when you are connected to a sewer connection. When you allow the water to drain away, the solids will accumulate inside the tank causing the dreaded “pyramid of poop.” In other words, without any liquid, the solid mass will accumulate and over time will cause the tank from draining.
  2. Leave the drain valve closed until the black water holding tank is nearly full.  This will give the solid matter time to break down, and the tank will more easily empty completely when the valve is opened. TIP: After you dump your tank and shut the valve back, put in 21oz. of Dawn Dishwashing Liquid. It is a grease cutter and will help keep your pipes clear and slick for easier dumping. 
  3. If your tiny house is stationary and more permanently connected to a sewer system or septic tank, it is still a good idea to clean your black water tank regularly to keep any build up down. The most effective way to do this is to just stick an old garden hose (the green kind) through the commode with as much water pressure as possible (just don’t use a pressure washer!) and spray water into the toilet being sure to hit all the nooks and crannies.

Face it. Storing used water, dumping used water, etc. just isn’t fun. It is necessary though and if you choose to live a nomadic life or rent out a tiny house with an otherwise un-conventional sewage system, you will need to know what black water is black, grey water is grey, and the garden hose isn’t as utilitarian as you once thought!

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