Source water characteristics and intake

You treat what the source gives you

Every choice a plant makes downstream, the coagulant, the filter, the disinfectant dose, starts with what comes in at the intake. The exam tests whether you can read a source and say what treatment it demands. That is a different skill than running the plant you already know, because your plant was built for one source, and the exam asks about sources unlike yours.

Surface water versus ground water

The first split is the one the whole exam hangs on. Surface water, from a river, lake, or reservoir, is exposed: it swings with rain and season, carries turbidity and organic matter, and is assumed to hold pathogens, so it gets the full treatment train of coagulation, sedimentation, filtration, and disinfection. Ground water from a protected aquifer is steadier and clearer, often safe with disinfection alone, but it can carry hardness, iron and manganese, arsenic, or nitrate that drive their own treatment.

The trap in the middle is ground water under the direct influence of surface water, GWUDI. A well close to a stream or with surface-like microbiology is regulated as surface water and must filter, even though it comes from the ground. Knowing why a source is classed GWUDI is a common exam point.

The raw-water numbers that drive treatment

A handful of source-water parameters decide what the plant has to do:

• turbidity, in NTU, the cloudiness that sets the coagulant and the filter load, and the headline number on a surface source
• total organic carbon and color, the disinfection-byproduct precursors that more chlorine alone makes worse
• alkalinity, the buffer coagulation needs; a low-alkalinity source needs lime or soda ash to coagulate
• temperature, which slows coagulation, settling, and disinfection in cold water, so winter is the hard season
• pH, which sets coagulation range and how chlorine behaves
• hardness, iron, manganese, arsenic, and nitrate, the ground-water contaminants that add softening, oxidation, or removal steps
• the pathogens, Giardia and Cryptosporidium especially, that are the reason surface water is filtered at all

Keep the source clean first

The cheapest treatment is the contamination that never reaches the intake. Watershed protection for surface sources and wellhead protection for ground sources are the first barrier in the multiple-barrier approach, and a source water assessment maps what threatens your supply. The exam frames source protection as treatment, not as something separate from it.

The rules that ride on your source

Your source type decides which federal rules apply. Surface water and GWUDI fall under the Surface Water Treatment Rules and their later versions, which require filtration and a disinfection CT credit against Giardia and viruses, with the Long Term 2 rule adding Cryptosporidium. Ground water falls under the Ground Water Rule, which targets fecal contamination of wells. Both sit on top of the maximum contaminant levels every system meets. The state, as the primacy agency, classifies your source and sets the monitoring.

Where operators lose points

• treating a ground source and a surface source as if they need the same train
• missing why a well is classified GWUDI and therefore must filter
• forgetting that cold water slows coagulation and disinfection, so winter doses and times change
• confusing operational source turbidity with the regulated combined-filter-effluent limit at the other end of the plant

Quick reference

• Surface water: variable, turbid, pathogen-prone, gets the full treatment train.
• Ground water: steadier and clearer, often disinfection only, but watch hardness, iron, manganese, arsenic, nitrate, and GWUDI.
• Raw-water drivers: turbidity, organic carbon and color, alkalinity, temperature, pH, the metals, and the pathogens.
• Protect the source first; it is the first barrier.
• Surface and GWUDI answer to the Surface Water Treatment Rules; ground water answers to the Ground Water Rule.

Where this fits

This is the front end of the water treatment exam. What you do with the water once it is in starts with coagulation and flocculation. The pathogens behind the rules are in the microbiology guide, the rules themselves in the regulations guide, and whatever your specific state adds on top lives at your state's page.