In an emergency get yourself to the Accident and Emergency Ward of the nearest hospital. Sometimes it's got flouride added. If in doubt boil the water for 5 minutes. Some say the risk of getting giardia is neglidge if take water from the surface of clear undisturbed streams. These maps are available from tourist information centres and petrol stations.
Topo maps are available from good camping and tramping stores.
Also, you not allowed to ride a bike on motorways. This is especially relevant to those riding in and out of Auckland which has several motorways. Find yourself a copy of the New Zealand Road Code or its cousin, the New Zealand Bicycle Code , available in libraries and bookshops. You must wear a helmet while riding on New Zealand roads. When tuning left you must give way to all other traffic.