Its no myth , I am still using spent resin to polish my water after RO down to 000 , the resin i am using is over 2 year old from when i had the T4 , when the Di became exhausted i stuck it in the shed and went to a 10 inch filter housing in the Fiat as a DI , that itself i have changed i think twice in 2 years , not because the TDS crept up but due to the fact it was quicker to renew than to rinse out the gunk , so i have used about 1.5 L of new resin in 2 years !