The Prophet ﷺ, was asked about water (in desert country) and what is frequented by animals and wild beasts. He replied: When there is enough water to fill two pitchers, it bears no impurity. (Using translation from Abū Dāʾūd 63)  

سُئِلَ رَسُولُ اللهِ ﷺ عَنِ الْمَاءِ وَمَا يَنُوبُهُ مِنَ الدَّوَابِّ وَالسِّبَاعِ؟ فَقَالَ «إِذَا كَانَ الْمَاءُ قُلَّتَيْنِ لَمْ يُحْمَلِ الْخَبَثَ»