Closing up a seasonal home: what actually causes the summer flood

Why an empty house is a different risk

Nothing on the list below is unique to vacant homes. Supply hoses fail in occupied houses too. The difference is entirely how long the water runs before anyone notices.

In an occupied home a failed washing machine hose is a bad afternoon. In a house closed up from May to October it is four months of mains-pressure water. That is the whole reason this page exists: the failure rate is the same, the consequence is not.

Arizona adds three specific aggravations. Heat: interior temperatures in a closed house left unconditioned through a Phoenix summer are extreme, and rubber, plastic and adhesive components degrade far faster at those temperatures. Hard water: mineral deposits sit on every valve seat and in every appliance, and a valve that has not moved in months is more likely to weep when it finally does. And a large seasonal population: a substantial share of housing across the Valley, Tucson, Prescott and the river towns sits empty for part of the year, which is why local plumbers see this failure pattern constantly.

There is also a plain insurance point worth knowing. Policies commonly treat damage in an unoccupied dwelling differently from damage in an occupied one, and some require the water to be shut off during extended absence. Reading your own policy before you leave is worth more than any advice here.

The five things that actually fail

When plumbers talk about what floods empty houses, it is a short list.

Washing machine supply hoses. The single most common cause. Rubber hoses harden and split, and they fail at full mains pressure with a large bore. Braided stainless is a cheap upgrade and shutting the valves behind the machine is free.

Water heater tanks and connections. Tanks corrode from the inside and eventually leak at the shell, and connections weep. A heater sitting hot and pressurized for months, unattended, in a hot garage, is doing nothing useful and taking on risk.

Toilet fill valves and supply lines. A fill valve that fails open sends water into the overflow continuously, which is not a flood but is a very large bill. A failed supply line is a flood.

Refrigerator ice-maker lines. Small-bore plastic tubing behind a heavy appliance, out of sight, often original to the fridge. It leaks slowly into flooring for months.

Angle stops and old valves under sinks. Compression stops that have sat for years frequently weep once disturbed or once pressure fluctuates.

Two things notably absent from that list: burst copper in walls, which is rare in the low desert outside a freeze; and slab leaks, which happen but are not more likely because a house is empty. The failures are at fittings, hoses and appliances, which is convenient, because all of them are downstream of a valve you can close.

Start with the main shutoff, and test it

Locating your main shutoff is not the same as having a working one, and this is where most closing-up routines quietly fail.

Arizona homes typically have one or two options: a valve on the house side, often in the garage, near the water heater, or on an exterior wall where the service line enters; and the meter valve at the street, which is the utility’s. Find the house-side valve, and then turn it. A gate valve that has not been operated in fifteen years in hard water may not close fully, may seize, or may weep from the stem once moved. Discovering that in October is fine. Discovering it during an emergency is not.

Then verify. With the main closed, open a tap at the lowest point in the house: it should run briefly and stop. Check the meter has stopped registering. If the meter still turns with the house valve closed, either the valve is not sealing or there is a leak between the meter and the valve, a service line problem, and a reason to call before you leave rather than after; see main water line repair.

Where a valve is seized or weeping, replacing it is a small job with an outsized payoff. A house whose main shutoff works is a house whose next emergency stays small. Adding a modern quarter-turn ball valve, ideally with a second isolation point, is one of the better hundred-dollar decisions available to a seasonal owner.

What to do with the water heater

This is where advice varies, and the right answer depends on how long you are away and what kind of heater you have.

Tank heaters, absence of a month or more. Turn the heater off, gas to pilot or off per the manufacturer’s instruction, electric off at the breaker, and close the cold inlet valve. That removes both the heat and, with the inlet closed, the pressure feeding the tank. Whether to drain the tank is a judgement: a drained tank cannot flood, but draining and refilling stirs sediment and, on an older tank, sometimes reveals a drain valve that will not reseal. For a heater in reasonable condition and an absence of a few months, off and isolated is the common approach; for a very old tank, or a heater in a location where a leak would be catastrophic, draining is the cautious choice.

Electric heaters especially: never leave the elements powered with the tank drained or partly drained. Dry-firing destroys an element in minutes. Breaker off before anything else.

Tankless heaters. There is no stored water to worry about, which is one of their genuine advantages here. Isolate the water and follow the vacation-mode instruction for the unit. If you are in the high country and the property will be unheated below freezing, tankless units need their specific freeze precautions followed, they contain a small volume of water in a heat exchanger that is expensive to replace. See tankless descaling and maintenance.

One local aside: a heater in an uninsulated Phoenix garage runs hotter and works harder all summer for no benefit while you are gone. Turning it off is both a risk reduction and a genuine saving.

Draining down, traps and the smell you come back to

With the main closed, opening taps at the highest and lowest points lets the system depressurise and drain the easy water. That is worth doing: it means a fitting that lets go while you are away has far less to deliver.

Full winterisation, blowing lines out and adding antifreeze to traps, is a high-country and freezing-climate procedure. In the low desert it is unnecessary, and it introduces its own risks. Do not confuse the two. In Prescott, Flagstaff-adjacent areas, the White Mountains or anywhere the house will sit unheated below freezing, it is a legitimate requirement and worth having done properly.

Traps are the other half of the story, and the reason so many returning owners meet a sewer smell at the door. Every drain has a water seal in its trap; over months in a hot, dry house that water evaporates and the seal is lost, letting sewer gas into the room. The fix is simple prevention: pour a little mineral oil into seldom-used traps, guest baths, floor drains, laundry, after topping them with water. The oil floats on the water and slows evaporation dramatically. It costs almost nothing.

Also worth doing: run the washing machine and dishwasher empty and leave their doors ajar, so neither sits wet and closed for months, and close the toilet lids on toilets whose water will evaporate.

If the landscape has to keep watering

This is the specifically Arizona complication. Many owners cannot simply close the main, because the landscape will not survive the summer without irrigation.

The answer is to isolate the house rather than the property. Practically, that means the irrigation take-off stays live upstream of a house-side isolation point, and everything inside the building is shut off and drained down. Where the existing plumbing does not allow that split, and on many homes it does not, fitting a separate isolation valve is a small job that makes every future closure straightforward.

Two extra precautions if irrigation stays live. First, have the irrigation supply and backflow device checked before you leave, because a failure there runs unattended too, see outdoor and irrigation plumbing. Second, arrange for someone to look at the meter periodically; an underground irrigation leak in July is a very large bill and a very slow discovery.

And where irrigation does not need to stay on, say so plainly to whoever prepares the house. Closing the whole property down is simpler, cheaper and safer than a partial closure.

Softeners, filters and RO systems

Treatment equipment needs its own thought, because it holds water, cycles on a timer, and is often plumbed with small-bore tubing.

A water softener left in service will keep regenerating on schedule for months, using water and salt to no purpose, and a drain line or valve failure runs unattended. Most units have a bypass; putting the softener in bypass and isolating it is the usual approach, and it also spares the resin an unnecessary summer of cycling. See water softener installation.

A reverse osmosis system under the sink has small tubing, a storage tank and several push-fit connections, a classic slow-leak candidate. Isolate its feed. Membranes also do not benefit from sitting dry and stagnant for months, so plan on flushing the system when you return and expect to replace filters on a schedule based on the calendar rather than on use. See reverse osmosis drinking water.

Whole-house filtration should be isolated with the main. Note the date, because filter life is partly a function of time as well as volume.

Also worth remembering: ice makers and evaporative coolers both have water feeds that are easy to forget and easy to isolate.

Monitoring, and who is actually looking at the house

Two things reduce the length of an unattended leak, which is the only variable that really matters.

A leak detection device. A whole-house automatic shutoff valve with flow monitoring closes the water when it sees a pattern that looks like a leak, and reports it. For a home that must stay pressurized, because of irrigation, a tenant, or a caretaker’s access, this is the single most effective measure available. Simpler point-of-use sensors under sinks, behind the washer and near the heater are inexpensive and catch the most common failures.

A human being. Somebody with a key who walks the house periodically, looks at the meter, and knows where the shutoff is and how to close it. A neighbor, a property manager or a family member. Leave them the shutoff location, a photo of it, and a phone number for a plumber. That combination has saved more Arizona houses than any device.

Write it down and leave it on the panel: main shutoff location, water heater isolation, irrigation status, who to call. Whoever visits the house in your absence should not have to work it out.

Coming back and reopening the house

Reopening deserves the same care as closing, and it is where problems reveal themselves.

Open the main slowly. A sudden restoration of pressure into an empty system is how a marginal fitting becomes a burst one, and slow filling lets you hear a problem before you see it. Then walk the house with the water on and everything closed, and watch the meter: if it registers, something is leaking now.

Open supply valves one at a time, the toilets, the washer, the sinks, the ice maker, and look at each one after it is pressurized. Restore the water heater properly: on an electric tank, confirm the tank is full before restoring power at the breaker. Flush stagnant water through every fixture until it runs clear and cold, including outdoor bibs, and run the dishwasher and washing machine empty once. Top up traps and re-oil the seldom-used ones if the house will sit again.

Then look, deliberately, at the places where leaks hide: under every sink, behind the washer, around the water heater’s base and pan, at the fridge, and along the base of walls in bathrooms. Water that started while you were away has had time to be quiet about it, if anything looks or smells damp, that is leak detection rather than a wipe-down.

Many seasonal owners book two short visits, one to close the house properly, one to reopen it, and treat it as the cost of not thinking about the property all summer. That is a reasonable way to look at it.