City water can have chlorine in it, which can cause baby boas to regurgitate.
Some breeders use distilled water.
Others leave the city water out for at least 24 hours before they offer it to their reptiles. During this 24 hour period, the chlorine evaporates from the water. Another option is to filter the city water with an activated charcoal filter. Breeders using well water are safe from chlorine, but should test for water hardness, etc. The following advice is the industry practice for eliminating mites.