The waterfall is in the other direction from the church and the hotel. The entrance fee is $5 and you get a 0.5l bottle of water in the restaurant. It is a 5 minute walk from the parking lot to the waterfall. In summer this waterfall hardly has any water, so it doesn't make sense to go there. Very beautiful, untouched nature.
Entry to Popokvil Waterfall costs 2000 riel (just under 50 cents) per person. You can exchange the ticket for a small bottle of water. During the dry season, the waterfall carries very little water. However, it's still worth the detour if you're already in the area. The entrance fee is negligible.