First, you need the feat: Craft Wondrous item.
If you have that you need to buy the materials. The material always cost 1/2 the market price (what you would pay to get the finished completed usable item in a shop).
With your feat and a quiet area to work, you enchant a mundane item, into a magical tem.
After you spend 1 day (8 hours) per 1000 gold of the market price enchanting the item, you make a spellcraft check. The DC of the check is determined by the caster level of the item, and any prerequisites you DON'T meet.
For your item, the DC would be 5+1 (the item's CL is 1) if you don't have access to the spells bless water or Purify food/drink, then the DC would be +5 (+10 if you don't have either spell). You can get access to the spell either from you, you friends, or even wands/scrolls/ or potions (although it seems silly to use up a magic item to make a magic item). So if you don't have those spells, the spellcraft DC would be 16. I believe both of the spells are 0 level cleric or Druid spells, it should be easy to have a friend cast them for ou. In which case ou would need to make a DC 6 spellcraft check.
There are other rules, but those are the basics.
Firstly, command activated uses 1,800 gp as the multiplier, not 2,000.
So, Purify F&D would be 0.5x1x1,800 = 900.
Assuming that the Bless Water effect is also command activated:
1x1x1,800 = 1,800 gp divided by 5/2 = 720 gp
Cheaper gets x1.5: 720x1.5 = 1,080
Sum is 1,980.
That's it from the tables. Next step is to compare this item to other items in the game to see if the price is right. It's a smidgeon cheaper than the unlimited-use command activated Horn of Fog, so I'd probably let it run at the calculated price.
Since bless water has got costly material component (25 gp) you need to take that into account (see note 4 in the table).
In your case that amounts to 25*50 = 1250 gp.
While I cannot find the rules text to support it, this cost is normally not halved when creating magic items.
Generally speaking, the cost of the item to be enchanted is subsumed in the cost to craft of the item, so the cost of the chalice is already included.
Forgot one: non-slot item, so double the final price.
Purify Food and Drink: 0.5x1x2,000 = 1,000 gp.
(Not sure where you're getting "charges for continuous" use from)
Bless Water 2/day: 1x1x1,800/(5/2) = 720.
Lower cost at x1.5 is 720x1.5 = 1,080.
Current total: 2,080 gp.
Material component cost: 1,250 gp (you only need to pay for 50 components, not 75 which you would by including this earlier)
Current total: 3,330 gp.
Non-slot item (entire cost x2 - though whether this should come before material components is open to debate): 6,660 gp (if this happens first, it's 4,160 + 1,250 = 5,410)
Still expensive.