what are they doing?

we have some pretty strict water restrictions in melbourne (basically cars can only be washed in commercial car washes that follows restrictions, lawns can only be watered during a 2 hr period, twice a week and not with drinking water.....). after the past 2 rain storms (today and the other day) i've heard the neighbour's back hose spraying (on what sounds like the cement ground they have). why would someone feel the need to water the pavement and why would you feel the need to do it directly after rain? i'm pretty sure they don't have any rain tank (i'm not actually gonna peer my head over our 6 foot fence) which would mean that's good water that's just running down pavement and eventually ending up the the creek.