Whether drinking water with too little amniotic fluid helps depends on the cause of the low amniotic fluid.
If the amniotic fluid is low due to an abnormal blood state and the placenta is in a hypercoagulable state, drinking water will not help, but you can use suppository medication to increase the placental circulation and increase the amount of amniotic fluid.
If the amniotic fluid is low due to severe anaemia or other medical conditions resulting in inadequate effective circulation, drinking water may be of some help.
If fetal malformations occur, drinking water will not help and is required to terminate the pregnancy depending on the condition of the pregnant woman.