depends on how bad your source water is. It will be more concentrated in whatever particulate/dissolved solids are in there. For example, the chlorine and copper levels (picked them at random) will be much higher in the waste water than in your tap and if they are borderline high in your tap, they will be over the safe limit in the waste water.
I have heard of people tanking the waste water for gardens, lawns, swimming pools, outdoor ponds, ect to make use of the waste. You just need a large tank to collect the water with an overflow to a drain when the tank is full. You can't build up any pressure in the drain line else the system won't work well at all.