Jonah
we have a pug expert HDI (900kg payload) with a 650ltr tank - its well within limits. 650 tank only holds 600ltrs (checked this on the weighbridge)
600ltr water = 600kg
tank = 45kg
driver = 80kg
all other equipment = 50kg (nowhere near that, more like 20kg)
fuel = 50kg
total = 825kg
thats a full tank, driver and tank of fuel.
when it was on the weighbridge there was a full tank of water, fuel, myself and scrooge (guy that works for me)
GVW was 62kg within limit.
And remember you are using that water up all day long - buy an Expert HDI, 650 tank and away you go. If you have oney to burn consider a Brodex E650 and bargain with them, they will barter.