Patent infringement
<p>I am developing a portable water filtration system , but I don't want to patent the design or the technology as I want the technology to be an open-source hardware and software technology. So let's assume that I released my product on a certain date for sale , let's assume that the date is 18th March 2018 , but as I made my hardware's design to be open-source , so anybody can copy it. </p>

<p>So is it possible that somebody could patent my design and sue me laterwards for patent infringement even when my product sale started before the other person's patent application's date and that over the fact that my technology is completely open-source?? And is there any open-source hardware licence available ?? </p>

<p>A person can only patent their own original invention. If the technology which is the subject of the patent existed before it was filed, then the patent is not enforceable. This is called <a href="https://en.wikipedia.org/wiki/Prior_art" rel="noreferrer"><em>prior art</em></a>.</p>

<p>Note that the rights to a patent can always be placed in the public domain. Patent just means "make obvious" in Latin. So, if you obtain a patent, that does not necessarily mean you are blocking other people from using the technology. There are also <a href="https://patents.stackexchange.com/questions/5341/how-can-i-provably-put-something-in-the-public-domain-so-that-someone-else-can-n">various established ways for publishing your technology to guarantee that it is in the public domain</a>.</p>

<p>If your product sale or public disclosure of your idea occurred before the priority date of the other parties patent, then it would be considered prior art.   Being prior art means it could potentially be used to invalidate the other parties patent. </p>

<p>Could they possibly get a patent issued based on your ideas?  Yes, it's possible the examiner would fail to come across your invention in the public domain. 
Should they decide to sue you they would be unlikely to win if you have your documentation in order. </p>

<p>Don't make decisions based on fear.  </p>

<blockquote>
  <p>So is it possible that somebody could patent my design and sue me
  laterwards for patent infringement even when my product sale started
  before the other person's patent application's date and that over the
  fact that my technology is completely open-source?? And is there any
  open-source hardware licence available ??</p>
</blockquote>

<p>In copyright law (in the United States, under the <a href="https://en.wikipedia.org/wiki/Copyright_Act_of_1976" rel="nofollow noreferrer">Copyright Act of 1976</a> which took effect January 1, 1978), the default rule is that everything that is capable of being copyrighted is immediately and automatically protected by copyright and that filing a copyright registration only increases your legal remedies. So, in copyright, there is infringement in the absence of an open source license, and you must contribute your copyright to the public domain or open source license it to protect users of the copyrighted work.</p>

<p>In patent law, the default rule is that nothing is protected by patent law unless a patent application is <a href="http://www.patenttrademarkblog.com/critical-deadlines-if-patent-application-not-filed/" rel="nofollow noreferrer">promptly filed after an event that triggers the deadline to file it</a> (this is a somewhat complex and heavily litigated issue). Disclosure of the material aspects of a patent without applying of a patent within the required time period automatically puts it into the public domain so an open source licenses is not necessary to prevent patent liability. </p>

<p>This rule is primarily implemented through the <a href="https://en.wikipedia.org/wiki/Prior_art" rel="nofollow noreferrer">doctrine of prior art</a>. This doctrine can be invoked both in the patent application process (which concludes with a public notice during which the public can provide prior art and object to its issuance) and also as a defense to a patent infringement action. It can also be invoked in an action to have a patent that was issued cancelled administratively by the PTO (a procedure which is incidentally <a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=2945639" rel="nofollow noreferrer">facing a legal challenge as to its validity on constitutional grounds</a>).</p>

<p>In the application process, the burden of proof is on the patent applicant, while in the infringement defense and cancellation proceeding context, the patent is presumed valid and the burden of proof is on the challenger of its validity. But, in practice, burden of proof is rarely important, because there is evidence presented about the prior art that is not ambiguous. </p>

<p><a href="https://papers.ssrn.com/sol3/papers.cfm?abstract_id=118149" rel="nofollow noreferrer">About 50% of patent infringement lawsuits that go to trial result in a finding that the patent is invalid</a>, although this is, in part, because where the patent is clearly valid the cases rarely go to trial. This high invalidity percentage is also due to the fact that the bar necessary to have a valid patent has <a href="http://patentlaw.typepad.com/patent/2005/05/updated_busines.html" rel="nofollow noreferrer">risen rapidly in recent years</a>. In 2001, 45% of business method patent applications were granted. In 2004, the grant percentage had dropped to 11%. <a href="https://abovethelaw.com/2016/02/who-is-alice-and-why-is-she-driving-patent-attorneys-mad-as-hatters/" rel="nofollow noreferrer">Similarly</a>, in January of 2004, only a little more than 2% of patent applications were rejected on Section 101 grounds which governs what is patentable, but by July of 2015, that percentage was about 15%.</p>

<p>The only reason to have an open source license for a patentable design would be to prevent someone from fearing a copyright lawsuit from using a design that is derivative of the one that you disclose.</p>

patents intellectual-property