Septic Tank with Wastewater Treatment

How can a ​household ​implement a ​cost-effective ​septic tank ​which would ​treat ​wastewater for ​gardening ​purposes or for ​flushing ​toilets?  ​

Are there any ​commercial ​designs ​available? ​Otherwise, how ​can a septic ​tank with ​wastewater ​treatment be ​designed?  ​

Here in New ​Delhi, people ​are willing to ​participate, ​reuse and ​conserve water. ​What can the ​treated ​water from a ​septic tank ​safely be ​reused for and ​which ​technology can ​be used to ​treat it?