Question

Why do water pipes usually crack in winter

Answer 1

the crack is and then cut out the bad section allowing for that which you can not see (hairline cracks). You will probably need the correct size pipe and connectors (couplings S x S) and PVC cement and PVC primer, a fine saw for cutting the pipe. Dry fit everything making sure the new section of pipe is of the correct length. There is a small situation in which you need the flexibility in the old plumbing to be able to attach the new section. You just have to think it thru.

Answer 2

during winter the water pipes contract due to less temperature where the water inside expand it has the property of expanding at lower temperature like 4 degrees celsius thus the freezing water exerts pressure on the pipe.