Water storage.

Our reasoning and expectations behind this.
We have opted for several smaller 12L water rather than one large tank, as for us there seem to be more advantages to using this system (see pros & cons below).
This size/shape of the container was chosen to fit where the current fuel tank is when that part of the van gets modified (see the extended floor where the fuel tank was) at present, we just put the containers we need in the van.
Currently, we have 12 containers available, 6 of which should fit under the rear seat leaving 6 spares (long-term replacement in case they go out of production).
Putting the containers in this position (all the other lower places on the van are spoken for) will help keep the extra weight as low and close to the center of the van as possible, whilst still being accessible.
We expect, most of the water will be used for personal consumption but on more remote trips we can take extra for use on the van if necessary.

The water storage containers.

12 containers of approximately 12L each, (not all will be used at the same time).

Once the rear floor is modified we are hoping to be able to fit up to 6 containers under the rear seat, giving us approximately 72L of water storage if required.

More info and Photos and a full write-up to follow soon.

In-use reviews.
Pros.

Several smaller containers will be easier to keep clean than one large tank.
The filling can be done (in most cases) straight from the tap.
Filling straight from the tap avoids possible contamination from hoses.
If one does get contaminated it isn’t the whole lot.
A container could be used to treat suspect water, in a reasonable quantity.
If containers aren’t needed for the trip, space is available for other items (more beer).
A small degree of weight redistribution is possible.
The containers are easily accessible from the inside.
Monitoring for contamination is easier, (especial as they are translucent).
Monitoring water usage is easier, (especial as they are translucent).
Water can easily be taken from the van.
The containers are easily drained.
No filler hole in the side of the van.
No hose to carry and to keep clean.
Water containers inside the van are less likely to freeze.
Not having a large water tank underneath leaves the space free for a fuel tank, (Planned).

Cons.

May take longer to fill.
The van sink & water heater connection will be less strait forward.
This size container could go out of production, (spares purchased).
The equivalent capacity single tank would be slightly smaller & lighter.
Water may degrade quicker in translucent containers, (store away from light if possible).

Our conclusions.
Other related or affected items.

Modified floor plan when the fuel tank is moved, (Planned).
Water filter,  (Available from home).
Water heater, (planned).
Pump from the water heater to an external shower-head, (planned).
Gas hob, sink, and cupboard units, (Under construction, Temporary).
Diesel hob, sink, and cupboard units, (Planned).