Tried a couple of variations on this recipe and have just a couple of suggestions. Use distilled white vinegar not cider vinegar unless you like very tangy ketchup. Tastes ok but if all you have is cider then for the first batch I'd reduce the amount in half. Maple syrup works great but other sweeteners do the job and shift the flavor a little. I tried Raw Sugar, Molasses, Agave Syrup and Maple Syrup. All gave a different taste but all were fine for me. Salt is salt unless you need kosher or flavored Himalayan salt but the tomato paste will drown out any variation on salt. I used Jane's Crazy Salt, but I got this from an organic foods sight so you do you. Water, unless you have chlorinated city water I wouldn't worry about it, We have a well. Garlic, I dosed it strongly as I like garlic. I did not find it necessary to cook it more than several minutes for desired thickness.
6oz Tomato Paste
1/2 C distilled white vinegar
1/4 C maple syrup
1/4 C filtered water
1 tsp sea salt
1/4 tsp onion powder
1/8 tsp garlic powder
Combine all ingredients over over medium heat and whisk until smooth.
Bring to a boil then reduce heat and simmer, stirring frequently scraping the sides
Simmer until desired thickness
Remove from heat and cool
Transfer to jar or glass bowl, cover tightly and refrigerate. Should last a month or so in the fridge. If you want to preserve this for long term storage use the hot water bath method and boil 15-20 min.