The video you are referring to of the 'tank fail' is the very first prototype crash tested system we sent along for exploratory testing of designs and to start to understand the forces involved in restraining a system.
It really does look catastrophic and is if there was no restraint at all - however that is definitely not the case. It was a modular tank design with 850litres of water in it with screw-on lids. It did have a restraint system which weighed about 90kg and was very securely mounted into the van. It was a low-level perimeter frame mounting system (as favoured by many DIYers) along with restraint bars through the moulded centre of the tanks - these were all fixed with 16mm bolts through floor into spreader plates under the floor. We learned a lot from this 'failure' and used it to greatly improve subsequent designs and MIRA tests.
What happened in the accident-test was:
1. The tanks collapsed under the weight of the water (this was despite being tank standard 6mm thick polythene) - this was because despite feeling very strong the tank itself is flexible in a crash and without full height restraint at the front can move too far forward.
2. Due to the collapsing pressure of the water the lids were blown off and the tank ripped apart.
3. Then under the strain of this forward movement the restraints bolts and spreader plates (1/4 the size of the current ones) started moving forward and sliced through the floor pan like a knife through butter destroying several cross members as it slid through them.
4. The system had moved completely out of the cargo area, through the cab area and then the forward moving water ripped through the engine bay bulkhead.
At the time I was not very pleased with the end result 
- however as a learning tool it was invaluable and taught me a new respect for carrying such a concentrated (most of the vehicle's load in just a 1/6th of its load area) and fluid (as in its ability to change shape) load.
What we did learn has been incorporated into the current Grippamax systems:
Non-Modular increased strength tanks
Burst-proof lids
Low level tanks
Full 'honeycomb' baffling
Full height restraint system
T-Bar front and rear restraint bars with large bonded spreader plates
There are of course many different ways of securing a tank of water in a van - it is always up to each user to risk assess their load, the van and their method of fixing. As long as they are happy with their choice then that is all that really matters (as long as they do not have an Employee sitting next to them 
)
We tread a fine line between securing a load in our vehicles and "fitting a system" in our vehicles? All similar in principle, but legally miles apart. The fitting of any system i've ever seen would not meet the legally required standards for securing a load.
I'll just do this loosley..........
A load is required to be restrained to the load bed, its also required to be against the bulkhead of the vehicle, if this is not possible, due to weight distribution or other, then physical obsticals should be put in place to ensure contact with bulkhead. The load should also not be capable of moving backwards (heavy acceleration).
A fitted system doesn't attract so much scrutiny. Like i said, most if not all are secured to the load bed through a series of bolts and spreader plates. So, where's the mystery, where's the magic, what makes the "proffesional fitted system better" ?
Well from what i can make out it all relys on a strong frame, bolted through the floor etc.. there is none of that "make sure the load cannot come foreward, so secure it against the bulkhead", as it appears at least in a physical sense at least, its not needed. The securing to the floor will suffice. For a fitted system............................
The amount of posts around this topic never fails to amuse me. "your safety", "think of your family", "A tonne of water behind your head"........etc. But in all them crash test videos i ever saw, the drivers legs where broke, his rib cage crashed in etc....and everyone wants to rave on....................the tank frame retained its integrity. Sure it did, that's what it was designed to do, in every vehicle.