The most commonly used water filtration technique involves coagulation and
rapid rate filtration, either in conventional plants with flocculation and
sedimentation, or in direct filtration plants in which the sedimentation pr
ocess is omitted. Both versions of coagulation and filtration can be effect
ive for controlling Giardia cysts and Cryptosporidium oocysts, but research
done by several investigators has shown that coagulation and filtration mu
st be operated very carefully to attain the best results. When filtered wat
er turbidity is 0.1 ntu or lower, the process is most effective. Careful co
ntrol of coagulation chemistry and of filtration rate increases, continuous
monitoring of filtered water turbidity, and proper management of backwash
water are keys to successful filtration.