No they are not. There are guidelines for how long you can store water samples until analysis. For example in the DIN/ISO norms or in the “Standard Methods for the Examination of Water and Wastewater”.

Water samples stored in open conditions for over a month are generally unsuitable for reliable testing. Microbial populations may grow or decay, chemical properties (e.g., pH, nutrients, or organics) can change due to oxidation or contamination, and physical properties may degrade. Most guidelines recommend analyzing samples within 24–48 hours, especially for microbiological tests, or preserving them properly (e.g., refrigeration at 4°C, sealing). For accurate results, fresh samples collected under proper storage and preservation protocols are essential.

Thank you all for your assist

i think you will get different results because of microorganisms activities