Accurate measurement of total lung capacity / vital capacity I'm currently working on a practical problem: How to measure your total lung capacity and/or your vital capacity accurately. Any suggestions or experience?
One of the methods that can be found with a quick google search is demonstrated in this video. You prepare a large water bottle by drawing a volume scale on its side. Then, you fill it with water, put it upside down into a sink and breathe into it via a tube. The air from your lungs will accumulate in the bottle and your scale will tell how many litres of water you replaced by air.
Another method is breathing into the microphone of your Smartphone... An app will evaluate the data. I am doubtful about the accuracy of this method. Any thoughts on this? 
Finally, there are some more aspects to consider. Lung capacity is not the amount of air you breath out after a deep inhale. That quantity is called vital capacity. The above mentioned techniques are measuring vital capacity rather than total lung capacity. Since it is impossible to breath out all the air in your lungs, can you even measure total lung capacity without medical equipment? While measuring the vital capacity is a good starting point, I am ultimately interested in total lung capacity.
The difference can be seen in this image from wiki - Lung volumes:

 A: After some experimentation and more research on the topic, I feel confident enough to present an answer. My initial concern seemed to hold true: There is no easy way to measure residual volume (RV) because you just cannot breathe out all of the air inside your lungs. You can use planimetry of chest radiographs, or plethysmography for that.
Concerning the measurement that I carried through: The smartphone apps were all extremely unreliable. They changed from smartphone to smartphone and showed a fluctuation of up to 50% on the same device. The video that I posted in the question is actually the most practicable way for me. Other possibilities mainly involved balloons (e.g. breathing into a balloon inside a container) but for the volume that I intended to measure (upwards of 5 liters), I couldn't find proper balloons and/or containers. 
Thus, my measurement setup was as follows: I prepared a 7.5 liter water jug just like they did in the video. I used coarse 1 liter steps for the first 5 liters, then made 0.1 liter tick marks until I reached 6.5 liters, and I ignored the rest. I put the jug upside down in a bucket and used a garden hose to breathe air inside the jug. I made lots of different "measurements" to look at normal breathing, deep inhaling and exhaling, etc. but ultimately I was just interested in vital capacity.
I have measured my own vital capacity to be 5.9 liters. It makes sense since I am still pretty young, I am 189 cm tall, and have an active lifestyle. I estimated the systematic error to be on the order of 0.2 liters (handling of the bottle, drawing of the scale, preparing of the setup), and reduced the statistical error by taking several measurements. Once I got the hang of "fully breathing out" (breathing out as much as possible), the value never really fluctuated by more than 0.1 liters. It doesn't seem to me that many people here  actually tried something similar or were interested in it, but if someone was interested and stumbled across this post, it would be helpful.
