1.9 non turbo engine won't have much power (70hp) but will get the job done.
The 1.9d has stood the test of time.
The 'clips' are probably just that and IMHO will not be man enough to secure a tank of water in the case of an accident. It would be much better to fit heavy duty ones with decent size spreader plates.
If you are thinking of purchasing one, then I would also look for a used Citroen, Peugeot or Fiat original full steel bulkhead. The tin plates that are available as an accessory are useless.
Make sure that all the keys work perfectly in all the locks and that the ignition has smooth operation. Replacing a barrel set and reprograming the ecu can be expensive.
Look for a well looked after van with a good service history and low mileage. If the outside looks great, but the cargo area looks like its been a builders van, be careful - I would walk away. If you aren't happy, move on.
Citroen introduced the Enterprise model to the lineup around this time - I see there were a couple on Ebay. Just be aware that the Enterprise model has ABS brakes. While that is great, finding used parts, ie wheel bearing hubs and drive shafts, will be very difficult as the majority broken for spares will be the non abs units.
Cleancare bought one about a year ago, so he may have some personal experience to add to this.