Refer to figure.
The presence on the runway of a fluid contaminant (water, slush or loose snow) or a solid contaminant (compacted snow or ice) adversely affects braking performance (stopping foce) by:

• Reducing the friction force between the tires and the runway surface; and
• Creating a layer of fluid between the tires and the runway, thus reducing the contact area and creating a risk of hydroplanning (partial or total loss of contact and friction between the tires and the runway surface).

=> Consequently, the landing distance will increase.

Regulation (EU) No 965/2012
CHAPTER 3 – PERFORMANCE CLASS B
CAT.POL.A.335 Landing – wet and contaminated runways Regulation (EU) 2019/1387
(a) When the appropriate weather reports or forecasts indicate that the runway at the estimated time of arrival may be wet, the LDA shall be one of the following distances:

(2) if a landing distance is not provided in the AFM for use on wet runways at time of dispatch, at least 115% of the required landing distance, determined in accordance with point CAT.POL.A.330(a);