background
canal
chemical
clean
concrete
corrosion
danger
dirty
drain
drainage
dump
ecology
environment
environmental
factory
flow
flowing
garbage
green
industrial
industry
liquid
natural
nature
old
pipe
pipeline
plant
polluted
polluting
pollution
polution
pond
problem
quality
river
rust
rusty
sewage
sewer
stream
substance
toxic
treatment
tube
unhygienic
urban
waste
wastes
water