"Buses and cars are standing by the water."
Translation:A víznél buszok és autók állnak.
Your version is the answer to the question "Where do buses and cars stand?" But in a weird way. As in "If I want to see buses and cars, where should I go?".
The above sentence, on the other hand, is the answer to the question "What is standing by the water?"
Your version would sound much natural with definite articles:
"A buszok és az autók a víznél állnak." - The buses and the cars are standing by the water.
But of course it all depends on what you want to say. :)