First Rain

LSI Lastem proposes the necessary equipment to divide the first rain from the following rain to support the realization of the “first rain” plants. The legislation provides that for some types of sites, there is a management of rainwater and washing of external areas for which there is, in relation to the activities carried out, a risk of pollutant run-off.

In particular, it is envisaged that a certain amount of water used for cleaning or rainfall on potentially polluted surfaces should not be released directly into the sewer system, but must first be accumulated in so-called “first rain” tanks and disposed of in the centralized treatment plant or treated in advance.

For first rainwater the first 5 mm are considered. of water evenly distributed over the entire draining surface rained over a certain period of time. When the 5 mm of rain is reached, the “further rain” phase begins. If the precipitation stops, before reaching 5 mm, after a programmed period, the “no rain” condition is passed. The start of precipitation is signaled by the DGP020 instrument which opens the contact until the cumulative 5 mm is reached, or upon the cessation of precipitation within the programmed period, when the contact is closed.

  • Complete detector / Intervention system, rain gauge and containment, feeding and fixing accessories;
  • Implementation of a contact (relay 1 A 250 V) depending on the state of precipitation: no rain, first rain, further rain;
  • Programming of rainfall event durations and amount of rainfall that determine precipitation states;
  • Indication of precipitation intensity;
  • Display for programming and for displaying the current status, including precipitation intensity;
  • Status indication LED;
  • Rain gauge according to WMO standard.

First Rain

Rain absence period:

is any period that includes at least T consecutive minutes of no precipitation. The beginning of precipitation during the absence of rain determines the passage to the condition of “first rain”.

First Rain

Period of first rain:

rainy period, following a period of rainless absence, continuous or with pauses of a duration of less than T minutes during which precipitation Qp mm occurred. When Qp mm of precipitation are totaled, the period of first rain ends with the transition to the condition of further rain. The possible occurrence, during the first rain, of a break longer than T2 minutes leads back to the condition of first rain.

First Rain

Period of further rain:

it is that period, after that of the first rain, during which there are never any precipitation pauses greater than T1 minutes. The finding of a pause longer than T1 minutes determines the transition to the rain absence condition.

The T1, T2 and Qp parameters are programmable.

documents LSI Lastem

First Rain


First Rain

Suitable Products

Sensori per misure meteorologiche

Meteorological sensors

Range of sensors for the measurement of the most typical meteorological quaintities. Connection to LSI LASTEM data loggers or third part systems



Range of digital display to display the quantities and convert the signals coming from the supplied sensors

Valeria Menichini

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