While trustable is a word, it is not used all that often. I would use trustworthy for both your examples: a source or person who is worthy of my trust.

@Selkie
I agree with you, "trustable" to me sounds like stumbling for the right word in some sentences and in others fits better than "trustworthy" that is why I am somewhat confused.

Please give me an example where you feel it fits better. I can't think of one at the moment.

I also had to think for a minute :)

It is a very trustable way of determining..........

I would have gone for "reliable" in that sentence ... ;-D

@ red hot
OK, I can't think of one at the moment :)

A little Google-skimming reveals that the times it is used there are often translations from other langauges, or a company that contains the name. I really think reliable, dependable are in more common use than trustable, which can be replaced with trusthworthy or trusty as well.

"Trustable" is NOT a word. (who are these people who say it is?)

Also, at least in current usage, "trusty" does not mean the same thing as "trustworthy". People can be trustworthy, but "trusty" is usually reserved for animals or things that are reliable in a less intentional, cognitive, or emotional way. "Trusty" has an antiquated ring to it, and usually it's used somewhat theatrically or ironically. (i.e. "my trusty steed", referring to a rusty but reliable bike)

@ Not it all-

trust /trʌst/ Pronunciation Key - Show Spelled Pronunciation[truhst] Pronunciation Key - Show IPA Pronunciation,
–noun
1.reliance on the integrity, strength, ability, surety, etc., of a person or thing; confidence.
2.confident expectation of something; hope.
3.confidence in the certainty of future payment for property or goods received; credit: to sell merchandise on trust.
4.a person on whom or thing on which one relies: God is my trust.
5.the condition of one to whom something has been entrusted.
6.the obligation or responsibility imposed on a person in whom confidence or authority is placed: a position of trust.
7.charge, custody, or care: to leave valuables in someone's trust.
8.something committed or entrusted to one's care for use or safekeeping, as an office, duty, or the like; responsibility; charge.
9.Law.
a.a fiduciary relationship in which one person (the trustee) holds the title to property (the trust estate or trust property) for the benefit of another (the beneficiary).
b.the property or funds so held.
10.Commerce.
a.an illegal combination of industrial or commercial companies in which the stock of the constituent companies is controlled by a central board of trustees, thus making it possible to manage the companies so as to minimize production costs, control prices, eliminate competition, etc.
b.any large industrial or commercial corporation or combination having a monopolistic or semimonopolistic control over the production of some commodity or service.
11.Archaic. reliability.
–adjective
12.Law. of or pertaining to trusts or a trust.
–verb (used without object)
13.to rely upon or place confidence in someone or something (usually fol. by in or to): to trust in another's honesty; trusting to luck.
14.to have confidence; hope: Things work out if one only trusts.
15.to sell merchandise on credit.
–verb (used with object)
16.to have trust or confidence in; rely or depend on.
17.to believe.
18.to expect confidently; hope (usually fol. by a clause or infinitive as object): trusting the job would soon be finished; trusting to find oil on the land.
19.to commit or consign with trust or confidence.
20.to permit to remain or go somewhere or to do something without fear of consequences: He does not trust his children out of his sight.
21.to invest with a trust; entrust with something.
22.to give credit to (a person) for goods, services, etc., supplied: Will you trust us till payday?
—Verb phrase
23.trust to, to rely on; trust: Never trust to luck!
—Idiom
24.in trust, in the position of being left in the care or guardianship of another: She left money to her uncle to keep in trust for her children.
[Origin: 1175–1225; (n.) ME < ON traust trust (c. G Trost comfort); (v.) ME trusten < ON treysta, deriv. of traust]

—Related forms
trust·a·ble, adjective
trust·a·bil·i·ty, noun
truster, noun

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Trustable is a word.