With an amber heat-health alert in force and the mercury pushing 35°C, your air conditioner or portable AC unit is working flat out. At the same time Wales is officially in drought after its driest July in almost 190 years, and hosepipe restrictions are spreading across the country. What almost nobody realises is that the very appliance keeping you cool is quietly making litres of water every day, most of which goes straight down the drain.

How much water it actually makes

In cooling mode an air conditioner, exactly like a dehumidifier, pulls moisture out of the warm air and drips it out as condensate. On a muggy day a portable unit can collect anywhere from one to three litres, and often more when humidity is high. The stickier the air, the more the unit strips out of it, so flats in humid coastal or city air fill the tank surprisingly quickly.

A fixed split system sends that water outside through a drain hose, but nothing stops you running that hose into a clean bucket instead of letting it drain away; a portable model catches it in an internal tank you empty as needed. Because it has passed over a cold coil, this water is effectively demineralised, close to distilled water, having lost its minerals. That makes it genuinely useful for some jobs and quietly risky for others.

Why you must never drink it

Here is the non-negotiable part: condensate water is not drinkable and should never go anywhere near cooking. As it trickles over the coils and sits in a tray it can pick up bacteria and biofilm, and standing water carries a legionella risk. With no minerals in it either, it is simply not fit to drink, and the same goes for your pets' bowl.

The safe habit is straightforward: collect it in a clean container and use it fresh rather than letting it sit for days.

Smart ways to put it to use

Free and mineral-free, condensate is ideal for exactly the tasks where tap water would leave limescale behind. The sensible uses are:

  • watering ornamental and non-edible plants;
  • flushing the toilet and washing hard floors;
  • topping up a steam iron, which actually prefers demineralised water;
  • topping up a car battery or the windscreen washer bottle.

The method is trivial: sit a clean container under the outlet or empty the portable unit's tank, and strain the water through a cloth before pouring it into an iron. Put like that, reusing a few free litres a day is a small but sensible move while hosepipe bans are in force. It will not refill a reservoir, but it costs you nothing.

What running the AC really costs

Now the honest bit: the water is free, but the air conditioner producing it is still adding to your electricity bill. At around 26p per kWh under the Ofgem price cap, plus the 57p daily standing charge, a 1kW portable unit costs roughly 26p an hour to run, so left on all day it can add more than a pound to your daily bill on its own. The condensate is a free by-product, in other words, not a reason to leave the cooling on longer than you need.

The real saving lies elsewhere: understanding how much your unit draws and running it efficiently. It is worth reading up on how air conditioning works, on the best ways to cut your electricity use during hot spells, and on coping with the heatwaves becoming a fixture of the British summer.