Do reed-beds cost a lot to run?

No, maintenance costs are very low.

Systems that operate by gravity and are not connected to an electrical supply have zero operating costs unless a gardener is emplyed to keep the beds free of weeds.

Flat site systems and others that use one or more pumps and are connected to an electrical supply will incur a running cost.  As the pumps only operate on demand this cost will be quite small.  For a 5 person system using a single pump the cost will be in the region of £15 per annum.

In both of the above systems the septic tank will need to be emptied on a regular basis. The recommendation is that this is done once a year, but, depending on the number of persons using the system the tank may not need emptying for 2-3 years.