If your car's cracks are full of dust & you have enough compressor power. Get an air duster/gun. I bought an Air Boy blower gun - Waterboy. They are pricey, I'm sure there are plenty of alternatives, but it is well made & I prefer to buy things once!

Go over the car with air only first & what's left over add water to clean off the remainder.

My 3 compressors will provide 40PSI continuously through this gun sucking up water at 0.5 litres per minute. So one can afford to use bottled water to wash the car!

A bit more compressor volume would be great which would push up the PSI a bit more with this gun, but what I have is adequate & with my small 4 litre air tank I have about 5 seconds at a higher PSI.

It is great to clean out all the cracks & corners, wipers, door hinges, roof gutters. I can blast into the boot hinge, because of the small amount of water I don't flood the car with the boot open as you would with water only.

It is the combination of air & water which cleans well. If you put your hand in front of the gun there is a very very slight abrasive feel to the water up close. 

I put a non return hose fitting on the bottom end of the pipe into the bucket, so when you stop the gun you don't waste air waiting for water to come back up the length of the hose. I  used an 18mm hose fitting & adapted it for a 6mm internal PVC tube, 5 metres long.

The boot hinge was full of dust, lots of dust around the light fittings. Up behind the under edge of rear window on this car fills up completely with dust & everytime you close the boot some more falls out. There are a few pieces of Velcro stuck around the car & it cleans them up nicely.

With preheated water it will make a good shower but with the slight abrasion be careful with cracks!