If you do CWE right its very safe. And its easy to tell if you have done it right, as the liquid should be pretty clear. Once its done, let it stand for 5 mins just to see if any white stuff settles at the bottom.
If you do Paramol which has DHC its a bit trickier as the coating on the tablet ,makes the water a bit cloudy. But this is where letting it stand is important, cus you can tell if the filtering has been effective.
DHC has less of a 'rush' but gets you more 'stoned' in my opinion. Hence I mix the two.
CWE is cheap and effective, and you should always do it. On top always have a anti histamine, you can get dirt cheap 99p pack of seven from boots. If you go over your limit fucking hell it can be brutal, but that more the 500+ when it can be savage!