You **can** fill a Mikva straight from a faucet, but the Mikva must be configured in a certain way, and rainwater is still required.  (This applies to all Mikvaot, not just for Keilim (dishes).)

According to the Sifra on Vayikra 11:36 and Zevachim 25b, if you have two pools, one filled with *kosher* water (eg, rainwater), and another filled with *pasul* water (eg. tap water), if they are connected by a pipe such that the waters connect, the *pasul* water becomes *kosher.*  This is known as **השקה.**  (See illustration **1** below.)  It is preferable that the pipe be made from a material that cannot become *tameh.*

There is a related concept called **זריעה,** which states that if you have two connected pools (as above), one empty, and one filled with *kosher* water, you can fill the empty pool by adding *pasul* water to the *kosher* pool, causing it to overflow.  (See illustration **2**.)

Due to various concerns (mostly about dilution), we add several *chumrot* to the process, and the final result looks like illustration **3**.

This type of setup makes cleaning the mikva and refilling the water much easier, as you only have to wait for the rain to fill the *kosher* pool once, and not every time you clean it.

*Disclaimer: This is the simplified version.  Mikvaot are complicated.  For practical applications, ask your rabbi.*

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![Illustration 1 - Hashke][1]

![Illustration 2 - Zeriah][2]

![Illustration 3 - Final Result][3]


  [1]: https://i.sstatic.net/3f3mZ.png
  [2]: https://i.sstatic.net/tBW6J.png
  [3]: https://i.sstatic.net/bd2Oq.png