Space: Sand filters occupy huge expensive space.
Redundancy & Associated Costs: Sand filter units need standby filters and multiple sets of backwash pumps, integration equipment, piping, valves, controls, etc.
Stopping for Backwash: Sand filters or other auto self-cleaning filters generally do not yield filtrate during backwash cycle.
Integration Logic, Automation: Sand filter installations are complex and feature multiple valves, interconnecting piping, gauges, pumps, automation panels, etc.
Quantum of Backwater Discharge: If suspended solids load is high, backwash frequency rises. Backwash effluent is often between 10-15% of inlet and at times even higher.
Algae: In warm countries, algae bloom fast. Sand filters choke frequently because algae settle and reproduce in the sand bed, finally requiring change of sand.
Electricity Consumption: Separate backwash pump, feed pump, multiple valves and other electrical equipments comprising sand filtration units consumes lot of power.
Sand needs to be replaced at regular intervals: Sand is expensive, and is an environmentally sensitive product, with diminishing availability.
Manpower: In a sand filtration unit, a person is needed to monitor and turn on and turn off the backwash cycle, and to occasionally replace sand.