Here is a simple English pachkhan wording for Porisi fast with water and medicine allowed:

“I take Porisi Pachkhan. Until the completion of Porisi, I will not eat any solid food. I will take only plain water, and I will take medicine if needed. I will observe this vow with full faith and sincerity.”

If you want, a slightly more formal version is:

“I undertake Porisi fast. Until the end of Porisi, I shall abstain from all solid food. I may take water and necessary medicine. I accept this vow with pure intention and devotion.”

You may also shorten it to:

“I take Porisi Pachkhan today: no food until Porisi is completed, but water and medicine are allowed.”

If you need, I can also give:

• a more traditional Jain-style English version
• a very short daily-use version
• a version for Ayambil, Ekasana, or Upvas