In intensive pig husbandry systems, pigs normally rest or lie on the solid floor and excrete on the slatted floor. This division changes when pigs are in heat stress. In heat stress, pigs move to the relatively cooler slatted floor for lying and, hence, excrete on the solid floor. Fouling of the solid floor leads to decreased hygiene conditions and increased ammonia emission in the pen, which has negative consequences for pig health and welfare. The aim of this study was to investigate whether a water spraying system on the slatted floor could aid pigs in heat stress to cool down and as a consequence they keep their lying area on the solid floor and their excretion area on the slatted floor. Twelve groups of 12 pigs (initial BW: 63.6±6.3 kg) were housed in 12 pens in a typical Dutch pig housing system. Each pen had a concrete slatted floor at the front of the pen (3.25 m2), then a solid floor (5.5 m2) and a metal slatted floor at the back (3.75 m2). In half of the pens, treatment pens, water was sprayed from a system installed above the slatted floor at the back of the pen. The spraying system was turned on once per hour for 50 seconds from 8:30 to 19:30 on every day. Control pens had no spraying system. Feed and water were accessible ad libitum. Percentage of pigs lying and number of excretions per pig per hour in the different areas of the pen were scored from video recordings on eight days in August 2015 (average inside temperature: 26.4±1.5 °C) by 15 min scan sampling and continuous observations, respectively. Behavioural observations of lying and excreting were analysed using restricted maximum likelihood. Pigs in the treatment pens lied on the metal slatted floor less than pigs in the control pens (18.0 vs 21.8% of total number of pigs, P<0.001). However, treatment pigs excreted more on the solid floor than control pigs (1.1 vs 0.8 times per hour per pen, P<0.01). More specifically, in the treatment pens, pigs excreted significantly more on the solid floor during the 30 min after the spraying system was activated compared to the 30 min before (5.5 vs 4.0 times per ten min in all observed pens, P<0.05) which was not seen in control pens. These results show that the spraying system was effective in keeping pigs to lie on the solid floor in times of heat stress, but it was not effective in reducing the number of excretions on the solid floor. It was hypothesized that increased activity on the slatted floor during and directly after spraying caused pigs to move to the solid floor for excretion.