The article discusses how pollution travels through sandy soils and gets purified along the way, focusing on the risk of contaminating groundwater in the Netherlands. Two types of soil pollution are considered: severe pollution from pit privies at camping sites and moderate pollution from river water used for groundwater recharge. The study shows that sandy soils can purify themselves enough to prevent groundwater contamination, as long as the soil is fine, dry, well-aerated, and the groundwater level is not too high or the infiltration rate is not too fast.