For example:
It's not safe to drink from PVC pipes, because PVC can leak poisons into the water.
Fracking can cause toxic chemicals to leach into ground water.
The translation I found was 滤去, but 滤 means to filter, so I'm not sure if that's the proper translation.
If you look at what Chinese website say about fracking, you can see for example:
报告认为，水力压裂可能出现的危险在于在压裂过程中可能出现液体溢出，压裂直接渗透到地下水资源中以及对废水的不当处理和排放等方面。
So CNPC uses 渗透 to say that the chemicals get into the ground water.
As for your other example regarding PVC:
生物污染主要是由于管材氧渗透和透光使管内的水介质滋生细菌；化学性污染主要来自于管道接触材料的渗透。
Again they use 渗透 to indicate how the chemicals/bacterial get into the water.
Note: As the comments note, some other ways you might say this could include 渗入 and 进入.
