Water level measurement in borewells

How to measure water level in a borewell

Hi, can anyone guide us on how to determine the water level inside a borewell? There is very less water yield say for about 2 minutes of water flow, in our 160ft old borewell which was dug 3 years ago in our unoccupied new house. So we decided to go for a new borewell which had very less flow at 60 feet while drilling, so we stopped immediately. After that there was all white rocky sand till 300 feet and we stopped it. After 2 days we sighted water till 20 feet and we did flushing process to check the static water level. During flushing water, we flushed for long time and the contractor assured there would be minimum 1000-1500 litres of water yield per day. Now it's one week after the process but we are not able to sight water in the borewell till 100 feet and not sure whether water is there in the borewell but we can hear a splashing sound when a small stone is dropped inside. We are located at Ottiyambakkam.