A sweet or sugary taste in tap water is one of the more common complaints and one of the least alarming, because it is almost always caused by dissolved minerals rather than by anything harmful. That said, it is worth working out which cause you have, because two of the possibilities point at your own plumbing rather than at the supply.
Minerals, the usual answer
Calcium, magnesium, sodium and bicarbonate all carry taste, and particular combinations read as sweet rather than as the flat or chalky character people expect from hard water. Elevated alkalinity in particular tends to be described as sweet or soft. This is why the same person can find one town's water sweet and another's sharp, and why a water softener changes the taste noticeably by swapping calcium and magnesium for sodium. None of it is a safety issue and none of it is a fault.
When it is a recent change
A taste that has appeared suddenly deserves more attention than one that was always there. Utilities switch sources seasonally and blend differently at different times of year, which changes mineral content and therefore taste, and a Consumer Confidence Report will tell you what the supply carries. The EPA requires every community water system to publish one annually and maintains a finder. A sudden change alongside discolored water, a smell or an advisory is a different matter and should go to the utility rather than into a filter.
Your own pipework and fittings
New copper pipework, recently soldered joints and new plastic pipe can all impart a taste for weeks after installation, and plastics in particular can read as sweet or faintly chemical while they cure. Water that has stood in the pipes overnight picks up more of whatever the plumbing gives it, which is why the first draw tastes different from water run for a minute. If the sweetness is worst on the first glass of the morning and clears after running the tap, the pipework is the cause and not the supply.
The cause people overlook
Taste is partly you. Medications, dental work, sinus infections and pregnancy all alter perception of taste and can make ordinary water taste sweet or metallic when nothing about the water has changed at all. The quick test is whether anyone else in the household notices, and whether bottled water tastes normal to you. If the sweetness follows you across different waters, the answer is not in the plumbing. If it is genuinely the supply and you simply dislike it, a carbon filter at the tap changes the character, and our drinking water filter guide covers the options.
Questions people ask about why does my water taste sweet
Is sweet tasting water dangerous?
Almost never. It is normally dissolved minerals such as calcium, magnesium and bicarbonate, which affect taste but are not a safety concern.
Why did it start suddenly?
Utilities blend and switch sources seasonally, which changes mineral content. New pipework and fresh solder joints also impart taste for weeks.
Why is it worse first thing in the morning?
Water standing overnight picks up more from the pipework. If running the tap clears it, the plumbing is the cause rather than the supply.
Could it be me rather than the water?
Yes. Medication, dental work, sinus infection and pregnancy all alter taste perception. If bottled water tastes sweet too, the water is not the cause.