Two tiny organisms present a big problem for New York City’s water department: cryptosporidium and giardia.

The city has spent $5 billion over the last five years combatting these organisms, which can cause fatal illnesses in the sick and elderly and gastrointestinal problems for those with healthy immune systems.

“In the city’s east-of-Hudson Croton watershed, where development has encroached on watershed land, federal regulators forced the city to filter the water; hence the $3 billion Croton filtration plant that recently opened,” City Limits reported.

The plant itself was a giant, politically fraught project.