Business owners, particularly in hospitality, are being advised to flush their water systems and check for pests before reopening this week.
The Ministry for Primary Industries (MPI) has listed a series of safety and hygiene checks for hospitality businesses.
The level 4 lockdown may have left many buildings with stagnant water stuck in pipes for up to nearly five weeks.
Hawke's Bay District Health Board drinking water assessor Reynold Ball said water could become stagnant if it was not regularly flushed through pipes, and this was likely to have happened during the level 4 lockdown.
Business owners should turn on all taps and flush toilets until the water was clear, he said.
That included piped-in systems for coffee and ice machines, and water intended for cleaning.
MPI said businesses should also check for pests, make sure fridges and freezers had not lost power, and check hygiene facilities were working.
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