lake water is safe to drink from a clean lake.
I have drank lake water when camping and it was much better tasting and healthier than city tap water.
I would recommend that you boil the lake water for a few minutes on a campfire or a stove in a pot before drinking it though.
Although the lake water is most likely safe to drink as is it's best to boil the water because there could potentially be bacteria in the lake water that could in rare cases make you sick.
So what I do is just boil the lake water and then allow it to cool down and then put it in the refrigerator of my camper trailer.
If I'm tent camping I put the lake water into the ice chest to cool down.
Once the water has cooled down enough I pour it into some water bottles and then put it in the ice chest.
Or I will pour some into a pitcher and place it in the camper refrigerator.