I don't need to test. Even if you call the water dept. Before you allow new water to come in contact with your Koi, check it. Add dechlor or aerate until there is no trace of chlorine. You may already have a quarantine tank and don't even know it.
Many ponds feature a small upper pool that feeds a stream that goes into the main pond.
Use this upper pool for your quarantine tank. You many need to alter your plumbing to allow the upper pool to be bypassed, but you should do this anyway so that you can bypass the waterfall in the winter. Use two filters in series. Periodically check the water coming out of the first filter. If it shows any trace of chlorine, change your media.