How water proof is the series 3 watch and is there a particular band that is better in water?

Hi

Apple advises that Apple Watch Series 3 models are sufficiently water resistant (they are not waterproof) that they can be used, for example, when shallow water swimming. They should not be submerged below shallow depth or exposed to high velocity water.

Detailed handling guidance in respect of water exposure, including cleaning and drying instructions, is provided by Apple here:

• About Apple Watch water resistance - Apple Support
• Important handling information

Leather and stainless steel bands are not water resistant and should not be worn when swimming. Some users have reported experiencing issues with the Sport Band having come undone during swimming, so you may prefer to use a band with a different type of fastening.

It is water resistant down to 50 meters. If you plan to swim with it I prefer the nylon models due to the buckle they use compared to the sport model. It is easier to have the sport one come off your wrist on impact with water.