Where to start

[Tarrel]

Be careful about your water supply. A filter, boiling, or chemical sterilisation will kill bugs, but your water may be chemically contaminated if it is fed by run-off from agricultural land (excess nitrates, pesticides, etc). The only way to remove these is by distillation of the water. You may be better looking at an alternative water source, such as rainwater collection. Worth checking what drains into your pond more carefully.

Hope this helps.