You absolutely mustn't drink from streams on the SWCP unless you have boiled the water or added purifying tablets. The SWCP is indeed a "wild strip" of varying width, and especially if it goes through National Trust or uncultivable land can be a haven for wildflowers, insects etc, but go a few hundred metres inland and you're often encountering some pretty intensive farming.
A couple of weeks ago on a hot day I set off from Port Isaac towards Tintagel and realised after about a mile that I'd forgot my water!! There were plenty of streams, but I thought staving off dehydration by getting e coli or cryptosporidium was a bad bargain, and aborted the walk.
I completed the walk today, and it was even hotter. I managed to cool down by immersing myself completely in.a stream pool just before it met the beach ( was wearing a swimming costume under my clothes), but it was full of scuzzy green weed, a sign of excess nutrients in the water (probably cow shit from the farms upstream. They shouldn't let the shit in the water. But they do :( )