Your Corn plant, Dracena, needs up-potting...I'd use a pot 2" larger than this pot. Is this a 6" pot? Go to a bit deeper and 2" wider diameter pot. Shake out the roots a bit and transplant using only potting soil. Get some Osmocote fertilizer (14-14-14) extended release. This is usually used 2 X per year for indoor plants. This guy needs fertilizer and a bit larger pot. In 3 months, you'll need a larger pot, 10" in diameter. To big a pot too soon will make most plants unhappy. No rocks, gravel at the bottom of a pot that HAS to have a drainage hole.
Use distilled water, once every 3 months put all your indoor plants into the shower, turn on the cold water and let them have a good 10-15 minute shower. Turn it off and allow these plant to drain, drip, dry off a bit...a couple of hours. No saucers allowed in their shower.
This ZZ plant is interesting. Looks quite healthy except this one branch. Cut that entire branch off at the beginning of that branch. Clean the scissors or pruners with alcohol. When this plant gets dry put in the shower for a good wash. If anymore leaves start doing this we will need to revisit!
Quit using tap water. Too many salts that will cause the tips of indoor plants and their margins to yellow and brown. The shower thing won't be a problem as it will add too little of the salts used once every 3 months. But get distilled water to water your plants with as by definition is JUST water. Only water the plants when the soil is dry, the corn plant will need more watering than the ZZ. Do you see any breakage at the bottom of that yellow branch? Any other leaves beginning to show any yellowing? Make sure you clean any pruner, scissors, fingers after touching this plant. Just being careful.