draw the water from the well and fill it in the 7ltr jar and then transfer the water in the 7ltr jar into 5ltr jar now you are left with 2ltrs of water in 7ltr jar and now empty the 5ltr jar and now tranfer the 2ltrs of water in 7ltr jar into 5ltr jar and again fill the 7ltr jar with water and now transfer the water in 7ltr jar into 5ltr jar ,we already hav 2ltr in 5ltr jar so only 3ltrs from 7ltr jar can be transfered so now you are left with 4ltrs of water in 7ltr jar now empty the 5ltr jar and transfer the 4ltrs of water left in 7ltr jar into 5ltr jar and now again fill the 7ltr jarand transfer the water into 5ltr jar as it already hav 4ltrs in 5ltr jar only ltr from 7ltr jar can be transfer so now ur left with 6ltrs of water in 7ltr jar .................

Another way
Fill 5 ltr first and transfer to 7 ltr jar
Fill again 5 ltr and transfer to 7 ltr jar -leaving 3 ltr in 5 ltr jar
Empty 7 ltr and transfer remaining 3 ltr from 5 ltr jar to 7 ltr jar
Fill 5 ltr and transfer to 7 ltr jar - leaving 1 ltr in 5 ltr jar
Empty 7 ltr jar and transfer 1 ltr from 5 ltr jar to 7 ltr jar
Fill again 5 ltr jar and transfer to 7 ltr jar - making it 6 ltr...