How to Sanitize an RV Fresh Water Tank

Drain everything, bypass the filter, add diluted unscented bleach, fill the tank, run it through every tap until you can smell it, let it stand, then drain and flush until the smell is gone. Do it at the start of each season and after any long storage.

Part of our sewer and water guide. For the dilution figures, use current guidance from the CDC or your trailer manufacturer's manual rather than a number from a forum — the ratios vary with bleach concentration, which has changed over the years.

Why bother

A fresh water tank is a dark, warm, wet plastic box that sits unused for months. Biofilm forms in exactly those conditions. It is why water from a trailer that has been stored over winter tastes wrong, and no filter fixes it because the problem is downstream of the filter.

It is also why people conclude their water filter is useless. The filter is fine; the tank is the issue.

When to do it

At the start of every season, after any storage longer than a month, when the water tastes or smells wrong, and after buying a used trailer — before you drink anything from it. That last one is not optional: you have no idea what the previous owner did.

What you will need

Unscented household bleach, a measuring jug, a funnel if your fill is awkward, and your drinking-water hose. Do not use scented bleach or any bleach with added cleaners.

Worth having before you start

A drinking-water hose you are confident in, a filter you can bypass and re-cartridge afterwards, and a regulator so the refill is not at full park pressure.

Best for The default fresh water hose

Camco TastePURE Drinking Water Hose (25 ft)

The correct part rather than an upgrade: a drinking-water-rated hose, in white so it never gets mixed up with the sewer gear.

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Best for Filtering that earns its housing

Camco EVO Premium RV Water Filter

A proper canister with a replaceable cartridge: better on sediment than the throwaway inline filters, and cheaper after season one.

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Best for The cheapest thing that prevents the worst damage

Camco Brass Water Pressure Regulator

The cheapest single item that prevents the most expensive damage. Fixed preset, brass body, screws on in four seconds.

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The steps in more detail

Drain everything first

Fresh tank, low point drains, and the water heater. Turn the water heater power off and let it cool before draining it — a hot tank being drained is a burn risk and can damage the element on some rigs.

Take the filter out of the circuit

Sanitizing solution will wreck a carbon cartridge. Either bypass the canister or remove the cartridge, and fit a fresh one at the end. If you are using a disposable inline filter, take it off entirely and fit a new one afterwards. See the water filter roundup.

Dilute in a jug, not in the tank

Mix the bleach with water in a jug first, then pour it in. Neat bleach poured straight into a tank sits concentrated at the bottom and can damage seals and fittings before it disperses.

Run it through every fixture

This is the step people skip and it is the step that matters most. The tank is not the only place biofilm lives — the lines, the pump, the water heater and the faucets all need treating. Open every tap, hot and cold, plus the shower and the toilet, until you can smell the solution at each one, then close it.

Let it stand, then flush properly

Follow the dwell time in your chosen guidance. Then drain, refill, and run every fixture again. Repeat until there is no smell anywhere. It commonly takes two full fills, and being impatient here means drinking bleach flavor for a week.

Doing it without bleach

Two reasonable alternatives if you would rather not use bleach.

A proprietary RV tank sanitizer. Sold specifically for this and dosed per gallon, usually with a shorter dwell time and less residual taste. Follow the product's own instructions.

Diluted white vinegar. Works on taste, odor and light scale, and is much gentler. It is not equivalent to bleach as a disinfectant, so treat it as a freshening step rather than a sanitizing one — useful mid-season, not a substitute for the start-of-season job.

What does not work is hoping. A tank that has sat all winter needs something done to it.

What goes wrong

Forgetting the water heater. It holds several gallons. If you do not drain and treat it, you have treated most of the system and left a reservoir of the problem.

Leaving the filter in. The cartridge is finished, and it will keep releasing the taste for weeks.

Not opening every tap. Treats the tank and leaves the lines. Half the job.

Under-flushing. Two full fills is normal. Stop when there is no smell, not when you are bored.

Using scented bleach. The scent additives are not meant for potable systems and the smell lingers in the plastic.