1. The plaintiff's incidental appeal and the defendants' appeal are all dismissed.

2. Costs of the appeal and incidental appeal shall be respectively made by each person.

1. The reasoning for the court's explanation concerning this case is as follows: (a) No. 2 of the first instance judgment, No. 19 of the first instance judgment, "An accident where inundation, etc. occurs (hereinafter "the accident of this case")." (hereinafter "the accident of this case") "the accident where flooding, etc. occurs (hereinafter "the accident of this case")" was present at the sixth hearing date of the first instance court on June 17, 2016, and the defendant C changed the location of the waterworks at the time when the construction of artificial test was requested to the defendant B. The defendant stated that "the above statement was made during the trial, but it is not sufficient to recognize that the previous statement was made against the truth and caused mistake, and there is no other evidence to acknowledge it differently); and (b) No. 3) "the occurrence of the liability for damages of this case" as stated in the main sentence of Article 420 of the Civil Procedure Act shall be cited as it is in accordance with the main sentence of Article 420 of the first instance judgment."

2. In light of the following circumstances acknowledged prior to the occurrence of liability for damages, namely, that there was no problem with the water pipes on the floor of the first floor of the instant building before Defendant B performed the construction of the instant water pipeline, and that the instant accident occurred due to the occurrence of the instant accident, it is reasonable to deem that the instant accident was caused by negligence, even though Defendant B had a duty of care to install water pipes so that water flows into the lower floor due to water leakage, etc., despite the fact that Defendant B had a duty of care to install water pipes so that water flows out on the lower floor.

Therefore, Defendant B is liable to compensate for damages incurred by the Plaintiff due to the instant accident.

In addition, the defect in the installation and preservation of a structure under Article 758(1) of the Civil Act refers to a state in which a structure does not have the safety to be ordinarily equipped according to its use.