TL;DR
Ice that tastes wrong is almost never the water -- it is a thin greasy film on the tray plus freezer odors absorbed into the plastic or silicone. Wash trays every two to four weeks in hot water with a degreasing dish soap, air them fully, and keep them covered in the freezer. Silicone in particular absorbs odor and needs the degreasing wash, not just a rinse.
Why ice ends up tasting like the freezer
Three things go wrong, usually together.
A grease film on the tray. Trays get handled with cooking hands and stacked next to open food. A microscopically thin layer of oil coats the surface and holds odor compounds against the water.
Absorbed odors in the material. Silicone is slightly porous at a molecular level and takes up smells from the freezer -- onions, fish, last month's leftovers. Soft plastics do this too. Ice frozen in that tray tastes of whatever the tray absorbed.
Sublimation. Ice slowly evaporates in a freezer even below freezing, and as it shrinks it concentrates whatever was dissolved in it while picking up circulating air. Old ice tastes stale for this reason alone.
Freezers also collect frost, spills, and drips, and an uncovered tray sits open to all of it. The film problem is the same one that plagues every silicone tool in a kitchen, which is why degreasing rather than scrubbing is the theme of the guide to cleaning kitchen tools without damaging them.
How do you clean ice cube trays?
Wash them in water as hot as your hands can comfortably stand with a degreasing dish soap, working a soft brush or a cloth into every cavity. Rinse thoroughly with hot water, then air dry completely upside down. For lingering odor, scrub with a baking soda paste or soak in a mild vinegar solution, rinse, and air the tray for a day.
The routine that works
1. Empty the tray and discard old ice. Ice more than a few weeks old will taste stale no matter how clean the tray is.
2. Wash hot with degreasing soap. Heat is what releases oil film. Warm water leaves it behind. A dedicated degreasing dish soap does far more here than extra scrubbing.
3. Get into every cavity. A soft bottle brush or a cloth wrapped over a fingertip reaches the corners where a sponge skims across the top.
4. Do the underside and the rim. Trays get stacked, so the outside picks up as much as the inside.
5. Rinse with hot water. Soap residue tastes worse than the original problem, and it is the most common cause of ice that tastes faintly bitter after a wash.
6. Air dry fully upside down. Water left in a cavity freezes into the first batch and carries any residual soap with it.
Getting stubborn odor out of silicone
Silicone trays are excellent at releasing cubes and unfortunately good at holding smells.
Start with a proper hot degreasing wash, which resolves most cases because the odor is usually riding on an oil film rather than embedded in the material.
If a smell survives that, make a thick paste of baking soda and water, coat the tray, leave it fifteen to thirty minutes, scrub, and rinse with hot water.
An alternative is a soak in a solution of one part white vinegar to three parts water for thirty minutes, followed by a thorough hot rinse. Use one method or the other -- there is no benefit to combining them, and cleaning products in general should be used one at a time.
Baking in a low oven is sometimes suggested for silicone bakeware, but it is not appropriate for ice trays, many of which are not rated for oven temperatures.
Finally, air it. Leave the tray out of the freezer, uncovered, in open air for a full day. Airing does more for absorbed odor than any wash. The same approach works on other silicone kitchen items, as covered in how to clean silicone baking mats and how to clean silicone and metal spatulas.
Are ice cube trays dishwasher safe?
Most silicone and hard plastic trays are dishwasher safe on the top rack, and a dishwasher does a good job on the grease film because of the water temperature.
Two cautions. Soft or thin plastic trays warp under dishwasher heat, and a warped tray leaks and stops releasing cubes cleanly. And a dishwasher that is itself carrying odors will transfer them to silicone, so a hand wash is sometimes the better choice.
Check the underside of the tray for a dishwasher safe mark before assuming.
Keeping ice tasting clean
Cover the trays. A lidded tray, or a zip bag over an open one, blocks most odor transfer and stops frost building on the surface of the cubes.
Store cubes in a sealed container. Ice left in an open bin in the freezer absorbs everything around it. Bag the cubes once they are frozen and refill the tray.
Use ice within two to three weeks. Older ice tastes stale from sublimation regardless of storage.
Keep raw foods sealed and separate. Odors travel through a freezer freely, and strong smelling items should be double wrapped.
Wash the trays on a schedule. Every two to four weeks for trays in regular use. It takes two minutes and it is easier than diagnosing bad ice later.
Clean the freezer itself occasionally. A wipe down with warm water and a little baking soda solution, plus removing anything spilled, addresses the source rather than the symptom.
Molds with lids follow the same rules, and their seals need extra attention -- see how to clean popsicle molds.
Washing trays reduces the residue and odor that make ice taste bad. It is not a food safety program on its own, and ice made from water that is itself a concern is a water quality question rather than a cleaning one.
Source: USDA Food Safety and Inspection Service guidance on freezer storage and food odors
FAQ
Why does my ice taste like the freezer?
Because odors travel through freezer air and get absorbed by the tray material and by the ice itself, usually helped along by a thin grease film on the tray. Wash trays hot with a degreasing dish soap, keep them covered, store cubes in a sealed bag, and use ice within a few weeks.
How often should you clean ice cube trays?
Every two to four weeks for trays in regular use. That interval keeps the grease film from building up to the point where it holds odor. Wash immediately if you notice the ice tasting or smelling off, and discard any ice already in the tray.
Can ice cube trays go in the dishwasher?
Most silicone and hard plastic trays can, on the top rack, and the high water temperature handles grease film well. Thin or soft plastic trays warp under dishwasher heat and should be washed by hand. Check the underside for a dishwasher safe mark first.
How do you get the smell out of a silicone ice tray?
Wash it hot with a degreasing dish soap first, since the odor usually rides on an oil film. If it persists, coat the tray with a baking soda paste for fifteen to thirty minutes, scrub, and rinse hot. Then leave it uncovered in open air for a full day.
Does old ice go bad?
It does not spoil, but it does taste stale. Ice slowly evaporates even in a freezer, concentrating whatever was dissolved in it and absorbing surrounding odors as it shrinks. Cubes older than about three weeks are usually worth replacing for taste alone.
Should you use hot or cold water to wash ice trays?
Hot, as hot as your hands can comfortably stand. The problem is a thin oil film, and warm water does not release it while hot water does. Rinse with hot water too, because soap residue left behind will taste worse than the original odor.
Trays take two minutes. Cleaning out the freezer and the kitchen around it takes considerably longer. If you would rather hand that off, get a quote or read more about house cleaning services.