Hi Stephanie It would be ...

Hi Stephanie

It would be helpful to know a little more as suggested in some of the other replies. What is the type of water? Are the tanks covered? Have you done any bacteriological tests?

The presence of sand and algae suggests only a problem of material accumulation. Is there any slime growth on the walls of the tanks?

Sediment can be removed by draining down the tank and simply scooping it up before rinsing and refilling the tank. You will need to make sure you don't disturb the sediment during this process. It is worth taking sensible precautions to avoid introducing contamination and use clean equipment, wear gloves etc. The tank could be filled and dosed with a little extra disinfectant to provide a residual to deal with any residual contamination but so the water was still fit for purpose (for example with water purification tablets). If there was any likelihood of faecal contamination (presence of animals or their droppings for example) then a more thorough disinfection would be necessary.

Also, consider what can be done to prevent sediment accumulation. Open tanks will permit algal growth and be exposed to wind blown sand. Keeping them covered, therefore, would be good. What about the water supply; there may also be a source of sediment from carry over from water treatment.

If there is any slime growth, the tank should be drained and the walls and base simply scrubbed clean, rinsed and flushed with clean water before being refilled with water for use. It may be possible to have some control over growth by maintaining a disinfectant residual in the water supply, if one does not exist.