No, brick slips are not waterproof.
Brick slips are made from real clay bricks. Clay is a porous material and does absorb water.
When installing brick slips in wet areas such as kitchens and bathrooms, we do recommend that a brick sealer is applied after installation. This offers some level of splash protection but does not make them waterproof.
There are waterproofing products available that can offer full protection. If you think you would need something along these lines, please let our team know and they will be able to offer advice on the best products to use.