Guides
Diagnostic guides: a symptom or a lab result in, a treatment class out, with the EPA or NSF limit cited by number.
Each guide starts from something you can see, smell or read off a test report, and ends at the class of equipment that fixes it. The regulatory limit is cited by number, and the sizing or part page that follows is linked from the guide.
Drinking water 16 pages
Diagnose
Brita vs PUR vs ZeroWater: certified lead, gallons
Brita Elite (WQA, 120 gal), PUR PLUS (WQA lead rows, 40 gal) and ZeroWater (IAPMO R&T, 15 gal) carry a certified lead claim; Brita Standard and plain PUR do not.
Diagnose
Water filter Black Friday and Prime Day deal check
A discounted water filter is a deal only if it carries NSF/ANSI 42, 53 or 58 for your contaminant in a certifier's listing. Black Friday: November 27, 2026.
Diagnose
Lead service line notice: what the letter means
The annual lead service line notice goes out by 31 December. What lead, GRR and unknown mean, and the 30-day clock you start by disputing the category.
Diagnose
Lithium in drinking water: no MCL, 10 ug/L HRL
EPA's UCMR 5 found 2,747 of 10,313 public water systems above the 10 ug/L lithium reference level. That level is a screening value, not an MCL.
Diagnose
UCMR 5: look up your water system's PFAS
EPA's final UCMR 5 dataset, released August 2026, covers about 10,130 water systems. Find your PWSID, read the result, and know why a non-detect means below 4 ppt.
Diagnose
Chromium-6 in California tap water: 10 ppb MCL
California's hexavalent chromium MCL is 0.010 mg/L (10 ppb), effective 1 October 2024. Compliance began 1 October 2026 for systems with 10,000 or more connections.
Diagnose
TDS meter reading: what it means, what is too high
A TDS pen reads conductivity times a factor, not contaminants. EPA's secondary standard is 500 mg/L; NHMRC rates 0 to 600 mg/L good for taste.
Diagnose
Reverse osmosis waste water ratio and drain
Under-sink RO wastes 4 to 5 gallons per gallon made per APEC. Whole-house RO reject should not go to a septic system, per UMN Extension.
Diagnose
Microplastics water filter: what removes them
EPA's draft CCL 6 (April 2026) lists microplastics with no limit. NSF/ANSI 401 is the only test: 85% reduction of 0.5 to 1 micron particles.
Diagnose
How to read a water test report: ND, MCL, units
A passed report means every MCL was met. Iron 0.3 mg/L, manganese 0.05 and pH 6.5 to 8.5 are unenforced secondary standards a lab may not flag.
Diagnose
EPA drinking water standards table: every MCL
Lead 15 ug/L action level, nitrate 10 mg/L, arsenic 0.010 mg/L, PFOA and PFOS 4.0 ppt, TDS 500 mg/L secondary: every EPA MCL and secondary standard, one table.
Diagnose
Does reverse osmosis remove it? Contaminant table
RO removes a contaminant only when its NSF/ANSI 58 or 53 listing names it: lead passes at 5 ppb, PFOA/PFOS at 20 ppt. Bacteria is NSF/ANSI 55 UV, not RO.
Diagnose
Reverse osmosis remineralization: do you need it?
RO strips 90 to 99% of dissolved solids per APEC. EPA's pH 6.5 to 8.5 and TDS 500 mg/L are ceilings with no mineral floor, so remineralize for taste.
Diagnose
PFAS in tap water: the 4.0 ppt limit and filters
EPA's 2024 rule sets PFOA and PFOS at 4.0 ppt. Only filters certified to NSF/ANSI 53 or 58 with a PFOA/PFOS claim are tested for it, to a 20 ppt protocol.
Diagnose
Lead in tap water: service lines and which filter
EPA's lead action level is 15 ppb, dropping to 10 ppb on 1 November 2027. Three checks find a lead service line; NSF/ANSI 53 or 58 filters pass at 5 ppb.
Diagnose
Fluoride in tap water: your level and which filters
Utah and Florida stopped adding fluoride in 2025; EPA's MCL stays 4.0 mg/L. How to read your CCR, and which filter classes reduce fluoride, and which do not.
Well water 16 pages
Diagnose
Well pump not working, no water: 6 checks
No water from a well: read the gauge against the switch cut-in (30 or 40 psi), check the breaker, the switch contacts, the tank pre-charge 2 psi below cut-in.
Diagnose
Well winter freeze checklist, part by part
A well freeze checklist: Minnesota code buries supply pipe 12 inches below the local frost depth, and a pitless adapter attaches 6 or 7 feet down.
Diagnose
Flooded well: what to do first, in order
A flooded well: power off and an electrician first, purge until clear, then disinfect, then a certified lab test at 7 to 10 days, 2 to 4 weeks and 3 to 4 months.
Diagnose
Uranium or radon in well water: limits and removal
EPA's uranium MCL is 30 ug/L, removed by anion exchange or RO. Radon in water has no final MCL, only a 1999 proposal; aeration vents it.
Diagnose
Arsenic in Well Water: Limit and Treatment
EPA's arsenic MCL is 10 µg/L (0.010 mg/L). Arsenic V leaves via RO, anion exchange or adsorptive media; arsenic III needs oxidation first.
Diagnose
Algae in water filter housing: cause and fix
Green growth in a clear housing is algae on light: fit an opaque sump. Rusty or oily slime is iron bacteria: shock chlorinate at 200 ppm max per MDH.
Diagnose
Sediment and turbidity in well water: which filter
Cloudy well water above 5 NTU shows in a glass (NDSU); UV needs under 1 NTU (VIQUA). Sand: a spin-down screen. Silt and clay: a 5 micron pleated cartridge.
Diagnose
Nitrate in well water: the 10 mg/L limit and fixes
Nitrate in well water above EPA's MCL of 10 mg/L as N (45 mg/L as nitrate) needs RO, anion exchange or distillation. Boiling and softeners remove none.
Diagnose
Coliform-positive well water: meaning and fixes
A coliform-positive well test means the sanitary barrier failed: shock chlorinate at up to 200 ppm, retest in 2 to 4 weeks, then UV at 40 mJ/cm2 if it returns.
Diagnose
What to test well water for: the annual panel
A private well needs coliform, nitrate, TDS and pH every year at a certified lab (CDC, EPA). Nitrate limit 10 mg/L as N. Which symptom adds which test.
Diagnose
Tea-colored well water: tannins vs iron, and fixes
Tea-colored well water that stays colored after a glass sits overnight is tannins, not iron. EPA lists color at 15 units; the fix is anion resin, carbon or RO.
Diagnose
Rotten egg smell in well water: hydrogen sulfide
Hydrogen sulfide has no EPA limit; the nose finds it at 0.05 to 0.1 mg/L. Hot tap only means the heater anode, both taps means the well, and the mg/L picks the fix.
Diagnose
Iron in well water: how much, and what treats it
Rust stains on a private well mean iron at or above the EPA secondary standard of 0.3 mg/L. Which form it is, and which treatment class fits each mg/L range.
Diagnose
How to shock chlorinate a well: amount and time
Shock chlorinate a well at 50 to 200 ppm with plain 6% or 8.25% bleach, hold it 2 to 6 hours or overnight, flush to 0 ppm, retest in 2 to 4 weeks.
Diagnose
Blue-green stains: low pH well water and the fix
Blue-green stains on a well are copper dissolved by low-pH water. EPA's pH range is 6.5 to 8.5; an acid-neutralizing filter treats down to pH 5.3.
Diagnose
Black stains from well water: manganese and fixes
Black stains on a private well mean manganese above EPA's secondary standard of 0.05 mg/L. Why it resists iron treatment, and which class fits each mg/L range.
Water softeners 11 pages
Diagnose
Water softener vs water filter: the difference
A softener swaps calcium and magnesium for sodium under NSF/ANSI 44 and leaves chlorine, lead and PFAS alone. A carbon filter (NSF/ANSI 42 or 53) does the reverse.
Diagnose
How long a water softener lasts: repair or replace
No maker document read here prints a lifespan. Pentair warrants Fleck valves 5 years; Dow gives resin 10 years under 0.2 ppm chlorine, 6 at 1 ppm.
Diagnose
Water softener Black Friday deal check: sizing
A softener deal is only real if the grain capacity fits: gpg (plus 5 per ppm iron) x people x 75 gal x days. The box number is the max-dose capacity.
Diagnose
Humidifier white dust: cause and what stops it
White dust from an ultrasonic humidifier is tap-water minerals in the mist, per EPA. Distilled or RO water stops it; softened water only swaps calcium for sodium.
Diagnose
Are water softeners banned where I live?
No US state bans residential water softeners. California HSC 116786 lets a local agency prohibit installation by ordinance, and only prospectively.
Diagnose
White flakes in water or ice: what they are
White flecks that fizz in vinegar are hardness scale: 1 gpg is 17.1 mg/L per MSU Extension. Floating plastic curls are dip tube; amber beads are resin.
Diagnose
Too much water in brine tank: normal level, causes
A brine tank holds about 1 inch over the grid (Fleck) or 2 to 5 inches (GE) by design. Higher means a plugged injector or drain line; check in that order.
Diagnose
Water softener not using salt: salt bridge diagnosis
A salt bridge is the usual cause. Pentair's 5600SXT manual says keep the tank below half-full, break the crust with a broom handle and wait 2 hours.
Diagnose
Fleck 5600SXT settings: capacity and hardness
Capacity = resin cu ft x grains per cu ft (1.0 cu ft at 8 lb = 22,000 grains), hardness in tested gpg, and metered regeneration, not a timer.
Diagnose
Salt-free water conditioner vs softener
An NSF/ANSI 44 softener drops hardness under 1 gpg. A TAC salt-free conditioner leaves it unchanged; its only pass mark is IAPMO Z601's 70% less-scale test.
Diagnose
White scale on faucets: how hard your water is
White crust on faucets and kettles is hardness scale. Hardness in gpg and mg/L (1 gpg = 17.1 mg/L), the USGS bands, and why 7.0 gpg is the line for a softener.
City water 4 pages
Diagnose
Wildfire water advisory: do not drink, do not boil
EPA says boiling wildfire-impacted water could create an inhalation risk until VOCs are ruled out. Benzene's federal MCL is 0.005 mg/L. Read the notice type first.
Diagnose
How to read your Consumer Confidence Report
A CCR is due by July 1 and covers mandatory monitoring only. The lead line is a 90th percentile of up to 100 homes, and data can be 5 years old.
Diagnose
Boil water notice: what boiling does not fix
CDC says 1 minute at a rolling boil, 3 above 6,500 feet. Boiling handles microbes and does nothing for lead, nitrate or PFAS. Here is the full procedure.
Diagnose
Chlorine or chloramine in city water: which carbon
EPA gives chlorine and chloramine the same 4.0 mg/L limit; only removal differs. Read the CCR, run a free-and-total strip, then pick the carbon.
Filters and cartridges 3 pages
Diagnose
Why is my tap water cloudy white? The glass test
Milky water that clears bottom-up in about 1 minute is dissolved air. Water that stays cloudy is turbidity; EPA caps public systems at 1 NTU.
Diagnose
Black specks after a new carbon filter: flush or test
Black specks after a filter change are carbon fines: GE says flush 2 to 3 gallons. Specks that outlast the flush point to manganese at 0.05 mg/L or rubber.
Diagnose
NSF/ANSI 42, 53, 58, 401, 55, 44, 177, 372 and P473
NSF/ANSI 42 is taste, 53 is health contaminants, 58 is RO at 75% TDS reduction, 55 is UV at 40 mJ/cm², and P473 is withdrawn into 53 and 58.
Reverse osmosis 3 pages
Diagnose
Reverse osmosis Black Friday and Prime Day deal check
Black Friday is November 27, 2026. Before buying RO on sale, check GPD at your pressure (APEC: 50 GPD at 60 psi, 30 at 50), drain ratio and NSF/ANSI 58.
Diagnose
Reverse osmosis water tastes bad: 5 causes by taste
Flat RO water is normal: NSF/ANSI 58 requires 75% TDS removal. Salty means the membrane, rotten egg means sanitize, chlorine the post-filter.
Diagnose
Reverse osmosis tank not filling: causes and fixes
RO tanks stop filling below iSpring's 45 psi feed minimum or with precharge under 5 to 10 psi empty. Six causes, the gauge check for each, the fix.
Refrigerator filters 2 pages
Diagnose
Generic vs OEM Fridge Filter: Check the NSF Listing
Neither OEM nor generic is certified by default. Look the model up at NSF, WQA or IAPMO: genuine EPTWFU01 is IAPMO-certified to 42, 53, 401; some generics 42 only.
Diagnose
Refrigerator Water Filter by Model Number
GE publishes no model-to-filter table. Read the old cartridge code, find the model number label, and route to the right cartridge across 6 brand families.
Whole-house systems 2 pages
Diagnose
Whole house filter and softener install order
Well: tank, sediment, iron fix, softener, carbon, UV last, since Viqua caps UV inlet at 7 gpg and 0.3 mg/L iron. City: sediment, carbon, softener.
Diagnose
Low water pressure after whole house filter: 4 causes
A 20 x 4.5 in Big Blue housing drops 1 psi at 15 gpm with 1 in ports and 2 psi with 3/4 in ports per Pentair. A gauge on each side finds the cause.