There are a variety of different designs and sizes for houseboats so there isn’t one answer for every houseboat. Since houseboats are made by a wide variety of manufacturers and sometimes even built by individuals there is no standard on what is included on every boat.
Most commonly, yes, there will be at least one bathroom on any houseboat as houseboats are designed to be used to sleep on for an extended period of time. Many people will stay on their houseboat for days or weeks and some people will even live on board so having a normal bathroom is important.
If your houseboat doesn’t have a toilet on board you can of course add one! There are portable marine toilets that you can buy or you can have one installed. With having a toilet on board you do have to have septic tanks on board for the toilet to drain into.
Of course once your tanks are full you will need to empty them somehow. Most marinas will have a pump out service that you can dock by and empty your tanks that way while other marinas will have a boat that floats around and empties the tanks while you are docked. Of course either way you will have to pay every time you empty your tanks.
Some houseboats will have two tanks on board one being gray water and one for black. The tank for gray water will have sinks or showers drain into it while the black water tank is for regular sewage. In many places the grey water tank can be emptied into the water while black of course can not.
If your boat goes into the ocean once you are more than 3 miles away from land surprisingly you can pump the raw sewage overboard as well. It is actually legal to empty your sewage tanks into the ocean since once you are more than 3 miles away from land the sewage will dissipate before reaching land (pretty gross isn’t it!).
Houseboat bathrooms can often be added at a later date if the boat that you purchase doesn’t come equipped with one. It will require tearing open some walls and running water and septic pipes so if you don’t have any plumbing experience it is better to hire a professional to install the plumbing than to do it yourself and end up with some sewage backing up because you didn’t do it correctly.
I personally prefer to have a couple of bathrooms if you have a larger houseboat or if you are going to have a bunch of people on board. If it is just you and your family then one bathroom would probably be plenty as you will just have to take turns using it.
If you want to know more about the way toilets and sewage work on your houseboat you can read all you’ve ever wanted to know (and more) in our article about sewage here.