Darren
Get hold of a tall bucket (e.g. a DIY beer fermentation bucket, or similar), about 16" high, and put your (smaller) water bucket inside this one.
Then when you are on the premises, take the water bucket out of the larger bucket and turn the larger bucket upside down and stand on it to reach that extra 16".
That way you do not need to carry 'A' frames or 'step-ups' around with you.
Also, while travelling between jobs, any water sloshing around in the small bucket will spill into the larger bucket and not onto the floor of your vehicle.
Mike